diff --git a/src/compute_group_group.cpp b/src/compute_group_group.cpp
index 79a6f63b90..a0bfbc34a7 100644
--- a/src/compute_group_group.cpp
+++ b/src/compute_group_group.cpp
@@ -16,6 +16,7 @@
 ------------------------------------------------------------------------- */
 
 #include "mpi.h"
+#include "string.h"
 #include "compute_group_group.h"
 #include "atom.h"
 #include "update.h"
@@ -41,7 +42,11 @@ ComputeGroupGroup::ComputeGroupGroup(LAMMPS *lmp, int narg, char **arg) :
   extscalar = 1;
   extvector = 1;
 
-  jgroup = group->find(arg[3]);
+  int n = strlen(arg[3]) + 1;
+  group2 = new char[n];
+  strcpy(group2,arg[3]);
+
+  jgroup = group->find(group2);
   if (jgroup == -1) error->all("Compute group/group group ID does not exist");
   jgroupbit = group->bitmask[jgroup];
 
@@ -52,6 +57,7 @@ ComputeGroupGroup::ComputeGroupGroup(LAMMPS *lmp, int narg, char **arg) :
 
 ComputeGroupGroup::~ComputeGroupGroup()
 {
+  delete [] group2;
   delete [] vector;
 }
 
@@ -64,6 +70,12 @@ void ComputeGroupGroup::init()
   pair = force->pair;
   cutsq = force->pair->cutsq;
 
+  // recheck that group 2 has not been deleted
+
+  jgroup = group->find(group2);
+  if (jgroup == -1) error->all("Compute group/group group ID does not exist");
+  jgroupbit = group->bitmask[jgroup];
+
   // need an occasional half neighbor list
 
   int irequest = neighbor->request((void *) this);
diff --git a/src/compute_group_group.h b/src/compute_group_group.h
index 9f37dd8c48..65d47e5fe6 100644
--- a/src/compute_group_group.h
+++ b/src/compute_group_group.h
@@ -28,6 +28,7 @@ class ComputeGroupGroup : public Compute {
   void compute_vector();
 
  private:
+  char *group2;
   int jgroup,jgroupbit,othergroupbit;
   double **cutsq;
   class Pair *pair;
diff --git a/src/fix_spring.cpp b/src/fix_spring.cpp
index 3cfc495a0f..1e985a8569 100644
--- a/src/fix_spring.cpp
+++ b/src/fix_spring.cpp
@@ -49,6 +49,8 @@ FixSpring::FixSpring(LAMMPS *lmp, int narg, char **arg) :
   extscalar = 1;
   extvector = 1;
 
+  group2 = NULL;
+
   if (strcmp(arg[3],"tether") == 0) {
     if (narg != 9) error->all("Illegal fix spring command");
     styleflag = TETHER;
@@ -66,12 +68,17 @@ FixSpring::FixSpring(LAMMPS *lmp, int narg, char **arg) :
   } else if (strcmp(arg[3],"couple") == 0) {
     if (narg != 10) error->all("Illegal fix spring command");
     styleflag = COUPLE;
+
+    int n = strlen(arg[4]) + 1;
+    group2 = new char[n];
+    strcpy(group2,arg[4]);
     igroup2 = group->find(arg[4]);
     if (igroup2 == -1) 
-      error->all("Could not find fix spring couple group ID"); 
+      error->all("Fix spring couple group ID does not exist"); 
     if (igroup2 == igroup) 
       error->all("Two groups cannot be the same in fix spring couple"); 
     group2bit = group->bitmask[igroup2];
+
     k_spring = atof(arg[5]);
     xflag = yflag = zflag = 1;
     if (strcmp(arg[6],"NULL") == 0) xflag = 0;
@@ -90,6 +97,13 @@ FixSpring::FixSpring(LAMMPS *lmp, int narg, char **arg) :
 
 /* ---------------------------------------------------------------------- */
 
+FixSpring::~FixSpring()
+{
+  delete [] group2;
+}
+
+/* ---------------------------------------------------------------------- */
+
 int FixSpring::setmask()
 {
   int mask = 0;
@@ -104,6 +118,15 @@ int FixSpring::setmask()
 
 void FixSpring::init()
 {
+  // recheck that group 2 has not been deleted
+
+  if (group2) {
+    igroup2 = group->find(group2);
+    if (igroup2 == -1) 
+      error->all("Fix spring couple group ID does not exist"); 
+    group2bit = group->bitmask[igroup2];
+  }
+
   masstotal = group->mass(igroup);
   if (styleflag == COUPLE) masstotal2 = group->mass(igroup2);
   
diff --git a/src/fix_spring.h b/src/fix_spring.h
index 0fb7df1dd4..a5b1f92c23 100644
--- a/src/fix_spring.h
+++ b/src/fix_spring.h
@@ -21,6 +21,7 @@ namespace LAMMPS_NS {
 class FixSpring : public Fix {
  public:
   FixSpring(class LAMMPS *, int, char **);
+  ~FixSpring();
   int setmask();
   void init();
   void setup(int);
@@ -36,6 +37,7 @@ class FixSpring : public Fix {
   double k_spring;
   int xflag,yflag,zflag;
   int styleflag;
+  char *group2;
   int igroup2,group2bit;
   double masstotal,masstotal2;
   int nlevels_respa;
diff --git a/src/group.cpp b/src/group.cpp
index 0b8196e08d..92fdaab220 100644
--- a/src/group.cpp
+++ b/src/group.cpp
@@ -21,7 +21,11 @@
 #include "atom.h"
 #include "force.h"
 #include "region.h"
-#include "memory.h"
+#include "modify.h"
+#include "fix.h"
+#include "compute.h"
+#include "output.h"
+#include "dump.h"
 #include "error.h"
 
 using namespace LAMMPS_NS;
@@ -44,9 +48,11 @@ Group::Group(LAMMPS *lmp) : Pointers(lmp)
 {
   MPI_Comm_rank(world,&me);
 
-  names = (char **) memory->smalloc(MAX_GROUP*sizeof(char *),"group:names");
+  names = new char*[MAX_GROUP];
   bitmask = new int[MAX_GROUP];
   inversemask = new int[MAX_GROUP];
+
+  for (int i = 0; i < MAX_GROUP; i++) names[i] = NULL;
   for (int i = 0; i < MAX_GROUP; i++) bitmask[i] = 1 << i;
   for (int i = 0; i < MAX_GROUP; i++) inversemask[i] = bitmask[i] ^ ~0;
 
@@ -54,7 +60,7 @@ Group::Group(LAMMPS *lmp) : Pointers(lmp)
 
   char *str = (char *) "all";
   int n = strlen(str) + 1;
-  names[0] = (char *) memory->smalloc(n*sizeof(char),"group:names[]");
+  names[0] = new char[n];
   strcpy(names[0],str);
   ngroup = 1;
 }
@@ -65,8 +71,8 @@ Group::Group(LAMMPS *lmp) : Pointers(lmp)
 
 Group::~Group()
 {
-  for (int i = 0; i < ngroup; i++) memory->sfree(names[i]);
-  memory->sfree(names);
+  for (int i = 0; i < MAX_GROUP; i++) delete [] names[i];
+  delete [] names;
   delete [] bitmask;
   delete [] inversemask;
 }
@@ -83,18 +89,49 @@ void Group::assign(int narg, char **arg)
     error->all("Group command before simulation box is defined");
   if (narg < 2) error->all("Illegal group command");
 
+  // delete the group if not being used elsewhere
+  // clear mask of each atom assigned to this group
+
+  if (strcmp(arg[1],"delete") == 0) {
+    int igroup = find(arg[0]);
+    if (igroup == -1) error->all("Could not find delete group ID");
+    if (igroup == 0) error->all("Cannot delete group all");
+    for (i = 0; i < modify->nfix; i++)
+      if (modify->fix[i]->igroup == igroup)
+	error->all("Cannot delete group currently used by a fix");
+    for (i = 0; i < modify->ncompute; i++)
+      if (modify->compute[i]->igroup == igroup)
+	error->all("Cannot delete group currently used by a compute");
+    for (i = 0; i < output->ndump; i++)
+      if (output->dump[i]->igroup == igroup)
+	error->all("Cannot delete group currently used by a dump");
+    if (atom->firstgroupname && strcmp(arg[0],atom->firstgroupname) == 0)
+      error->all("Cannot delete group currently used by atom_modify first");
+
+    int *mask = atom->mask;
+    int nlocal = atom->nlocal;
+    int bits = inversemask[igroup];
+    for (i = 0; i < nlocal; i++) mask[i] &= bits;
+
+    delete [] names[igroup];
+    names[igroup] = NULL;
+    ngroup--;
+
+    return;
+  }
+
   // find group in existing list
-  // igroup = -1 requires a new group, add it
+  // add a new group if igroup = -1
 
   int igroup = find(arg[0]);
 
   if (igroup == -1) {
     if (ngroup == MAX_GROUP) error->all("Too many groups");
-    igroup = ngroup;
-    ngroup++;
+    igroup = find_unused();
     int n = strlen(arg[0]) + 1;
-    names[igroup] = (char *) memory->smalloc(n*sizeof(char),"group:names[]");
+    names[igroup] = new char[n];
     strcpy(names[igroup],arg[0]);
+    ngroup++;
   }
 
   double **x = atom->x;
@@ -329,20 +366,20 @@ void Group::create(char *name, int *flag)
   int i;
 
   // find group in existing list
-  // igroup = -1 requires a new group, add it
+  // add a new group if igroup = -1
 
   int igroup = find(name);
 
   if (igroup == -1) {
     if (ngroup == MAX_GROUP) error->all("Too many groups");
-    igroup = ngroup;
-    ngroup++;
+    igroup = find_unused();
     int n = strlen(name) + 1;
-    names[igroup] = (char *) memory->smalloc(n*sizeof(char),"group:names[]");
+    names[igroup] = new char[n];
     strcpy(names[igroup],name);
+    ngroup++;
   }
 
-  // add atom to group if flag is set
+  // add atoms to group whose flags are set
 
   int *mask = atom->mask;
   int nlocal = atom->nlocal;
@@ -358,8 +395,20 @@ void Group::create(char *name, int *flag)
 
 int Group::find(const char *name)
 {
-  for (int igroup = 0; igroup < ngroup; igroup++)
-    if (strcmp(name,names[igroup]) == 0) return igroup;
+  for (int igroup = 0; igroup < MAX_GROUP; igroup++)
+    if (names[igroup] && strcmp(name,names[igroup]) == 0) return igroup;
+  return -1;
+}
+
+/* ----------------------------------------------------------------------
+   return index of first available group
+   should never be called when group limit has been reached
+------------------------------------------------------------------------- */
+
+int Group::find_unused()
+{
+  for (int igroup = 0; igroup < MAX_GROUP; igroup++)
+    if (names[igroup] == NULL) return igroup;
   return -1;
 }
 
@@ -373,10 +422,11 @@ void Group::write_restart(FILE *fp)
   fwrite(&ngroup,sizeof(int),1,fp);
 
   int n;
-  for (int i = 0; i < ngroup; i++) {
-    n = strlen(names[i]) + 1;
+  for (int i = 0; i < MAX_GROUP; i++) {
+    if (names[i]) n = strlen(names[i]) + 1;
+    else n = 0;
     fwrite(&n,sizeof(int),1,fp);
-    fwrite(names[i],sizeof(char),n,fp);
+    if (n) fwrite(names[i],sizeof(char),n,fp);
   }
 }
 
@@ -389,17 +439,22 @@ void Group::read_restart(FILE *fp)
 {
   int i,n;
 
-  for (i = 0; i < ngroup; i++) memory->sfree(names[i]);
+  // delete existing group names
+  // atom masks will be overwritten by reading of restart file
+
+  for (i = 0; i < MAX_GROUP; i++) delete [] names[i];
 
   if (me == 0) fread(&ngroup,sizeof(int),1,fp);
   MPI_Bcast(&ngroup,1,MPI_INT,0,world);
   
-  for (i = 0; i < ngroup; i++) {
+  for (i = 0; i < MAX_GROUP; i++) {
     if (me == 0) fread(&n,sizeof(int),1,fp);
     MPI_Bcast(&n,1,MPI_INT,0,world);
-    names[i] = (char *) memory->smalloc(n*sizeof(char),"group:names[]");
-    if (me == 0) fread(names[i],sizeof(char),n,fp);
-    MPI_Bcast(names[i],n,MPI_CHAR,0,world);
+    if (n) {
+      names[i] = new char[n];
+      if (me == 0) fread(names[i],sizeof(char),n,fp);
+      MPI_Bcast(names[i],n,MPI_CHAR,0,world);
+    } else names[i] = NULL;
   }
 }
 
diff --git a/src/group.h b/src/group.h
index c3cd6bd29e..74565a3d68 100644
--- a/src/group.h
+++ b/src/group.h
@@ -21,11 +21,8 @@ namespace LAMMPS_NS {
 
 class Group : protected Pointers {
  public:
-  int me;
-  int ngroup;                  // # of defined groups
   char **names;                // name of each group
   int *bitmask;                // one-bit mask for each group
-  int *inversemask;            // inverse mask for each group
 
   Group(class LAMMPS *);
   ~Group();
@@ -47,6 +44,13 @@ class Group : protected Pointers {
   void angmom(int, double *, double *);    // angular momentum of group
   void inertia(int, double *, double [3][3]);     // inertia tensor
   void omega(double *, double [3][3], double *);  // angular velocity
+
+ private:
+  int me;
+  int ngroup;                  // # of defined groups
+  int *inversemask;            // inverse mask for each group
+
+  int find_unused();
 };
 
 }