diff --git a/src/Pstream/mpi/UIPread.C b/src/Pstream/mpi/UIPread.C
index 14360e0cc0..fb6a9ec7d7 100644
--- a/src/Pstream/mpi/UIPread.C
+++ b/src/Pstream/mpi/UIPread.C
@@ -66,6 +66,14 @@ Foam::UIPstream::UIPstream
 
         label wantedSize = externalBuf_.capacity();
 
+        if (debug)
+        {
+            Pout<< "UIPstream::UIPstream : read from:" << fromProcNo
+                << " tag:" << tag << " wanted size:" << wantedSize
+                << Foam::endl;
+        }
+
+
         // If the buffer size is not specified, probe the incomming message
         // and set it
         if (!wantedSize)
@@ -75,6 +83,12 @@ Foam::UIPstream::UIPstream
 
             externalBuf_.setCapacity(messageSize_);
             wantedSize = messageSize_;
+
+            if (debug)
+            {
+                Pout<< "UIPstream::UIPstream : probed size:" << wantedSize
+                    << Foam::endl;
+            }
         }
 
         messageSize_ = UIPstream::read
@@ -127,6 +141,7 @@ Foam::UIPstream::UIPstream(const int fromProcNo, PstreamBuffers& buffers)
     if (commsType() == UPstream::nonBlocking)
     {
         // Message is already received into externalBuf
+        messageSize_ = buffers.recvBuf_[fromProcNo].size();
     }
     else
     {
@@ -134,6 +149,14 @@ Foam::UIPstream::UIPstream(const int fromProcNo, PstreamBuffers& buffers)
 
         label wantedSize = externalBuf_.capacity();
 
+        if (debug)
+        {
+            Pout<< "UIPstream::UIPstream PstreamBuffers :"
+                << " read from:" << fromProcNo
+                << " tag:" << tag_ << " wanted size:" << wantedSize
+                << Foam::endl;
+        }
+
         // If the buffer size is not specified, probe the incomming message
         // and set it
         if (!wantedSize)
@@ -143,6 +166,12 @@ Foam::UIPstream::UIPstream(const int fromProcNo, PstreamBuffers& buffers)
 
             externalBuf_.setCapacity(messageSize_);
             wantedSize = messageSize_;
+
+            if (debug)
+            {
+                Pout<< "UIPstream::UIPstream PstreamBuffers : probed size:"
+                    << wantedSize << Foam::endl;
+            }
         }
 
         messageSize_ = UIPstream::read
@@ -180,6 +209,14 @@ Foam::label Foam::UIPstream::read
     const int tag
 )
 {
+    if (debug)
+    {
+        Pout<< "UIPstream::read : starting read from:" << fromProcNo
+            << " tag:" << tag << " wanted size:" << label(bufSize)
+            << " commsType:" << UPstream::commsTypeNames[commsType]
+            << Foam::endl;
+    }
+
     if (commsType == blocking || commsType == scheduled)
     {
         MPI_Status status;
@@ -214,6 +251,14 @@ Foam::label Foam::UIPstream::read
         label messageSize;
         MPI_Get_count(&status, MPI_BYTE, &messageSize);
 
+        if (debug)
+        {
+            Pout<< "UIPstream::read : finished read from:" << fromProcNo
+                << " tag:" << tag << " read size:" << label(bufSize)
+                << " commsType:" << UPstream::commsTypeNames[commsType]
+                << Foam::endl;
+        }
+
         if (messageSize > bufSize)
         {
             FatalErrorIn
@@ -256,6 +301,15 @@ Foam::label Foam::UIPstream::read
             return 0;
         }
 
+        if (debug)
+        {
+            Pout<< "UIPstream::read : started read from:" << fromProcNo
+                << " tag:" << tag << " read size:" << label(bufSize)
+                << " commsType:" << UPstream::commsTypeNames[commsType]
+                << " request:" << PstreamGlobals::outstandingRequests_.size()
+                << Foam::endl;
+        }
+
         PstreamGlobals::outstandingRequests_.append(request);
 
         // Assume the message is completely received.
@@ -267,7 +321,8 @@ Foam::label Foam::UIPstream::read
         (
             "UIPstream::read"
             "(const int fromProcNo, char* buf, std::streamsize bufSize)"
-        )   << "Unsupported communications type " << commsType
+        )   << "Unsupported communications type "
+            << commsType
             << Foam::abort(FatalError);
 
         return 0;
diff --git a/src/Pstream/mpi/UOPwrite.C b/src/Pstream/mpi/UOPwrite.C
index f8439ba517..9f8726d9a0 100644
--- a/src/Pstream/mpi/UOPwrite.C
+++ b/src/Pstream/mpi/UOPwrite.C
@@ -43,6 +43,14 @@ bool Foam::UOPstream::write
     const int tag
 )
 {
+    if (debug)
+    {
+        Pout<< "UIPstream::write : starting write to:" << toProcNo
+            << " tag:" << tag << " size:" << label(bufSize)
+            << " commsType:" << UPstream::commsTypeNames[commsType]
+            << Foam::endl;
+    }
+
     bool transferFailed = true;
 
     if (commsType == blocking)
@@ -56,6 +64,14 @@ bool Foam::UOPstream::write
             tag,
             MPI_COMM_WORLD
         );
+
+        if (debug)
+        {
+            Pout<< "UIPstream::write : finished write to:" << toProcNo
+                << " tag:" << tag << " size:" << label(bufSize)
+                << " commsType:" << UPstream::commsTypeNames[commsType]
+                << Foam::endl;
+        }
     }
     else if (commsType == scheduled)
     {
@@ -68,6 +84,14 @@ bool Foam::UOPstream::write
             tag,
             MPI_COMM_WORLD
         );
+
+        if (debug)
+        {
+            Pout<< "UIPstream::write : finished write to:" << toProcNo
+                << " tag:" << tag << " size:" << label(bufSize)
+                << " commsType:" << UPstream::commsTypeNames[commsType]
+                << Foam::endl;
+        }
     }
     else if (commsType == nonBlocking)
     {
@@ -84,6 +108,15 @@ bool Foam::UOPstream::write
             &request
         );
 
+        if (debug)
+        {
+            Pout<< "UIPstream::write : started write to:" << toProcNo
+                << " tag:" << tag << " size:" << label(bufSize)
+                << " commsType:" << UPstream::commsTypeNames[commsType]
+                << " request:" << PstreamGlobals::outstandingRequests_.size()
+                << Foam::endl;
+        }
+
         PstreamGlobals::outstandingRequests_.append(request);
     }
     else
@@ -93,7 +126,8 @@ bool Foam::UOPstream::write
             "UOPstream::write"
             "(const int fromProcNo, char* buf, std::streamsize bufSize"
             ", const int)"
-        )   << "Unsupported communications type " << commsType
+        )   << "Unsupported communications type "
+            << UPstream::commsTypeNames[commsType]
             << Foam::abort(FatalError);
     }
 
diff --git a/src/Pstream/mpi/UPstream.C b/src/Pstream/mpi/UPstream.C
index b5a76e36e9..3623f5da58 100644
--- a/src/Pstream/mpi/UPstream.C
+++ b/src/Pstream/mpi/UPstream.C
@@ -70,6 +70,12 @@ bool Foam::UPstream::init(int& argc, char**& argv)
     MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
     MPI_Comm_rank(MPI_COMM_WORLD, &myProcNo_);
 
+    if (debug)
+    {
+        Pout<< "UPstream::init : initialised with numProcs:" << numprocs
+            << " myProcNo:" << myProcNo_ << endl;
+    }
+
     if (numprocs <= 1)
     {
         FatalErrorIn("UPstream::init(int& argc, char**& argv)")
@@ -124,6 +130,11 @@ bool Foam::UPstream::init(int& argc, char**& argv)
 
 void Foam::UPstream::exit(int errnum)
 {
+    if (debug)
+    {
+        Pout<< "UPstream::exit." << endl;
+    }
+
 #   ifndef SGIMPI
     int size;
     char* buff;
@@ -164,6 +175,11 @@ void Foam::UPstream::abort()
 
 void Foam::reduce(scalar& Value, const sumOp<scalar>& bop)
 {
+    if (Pstream::debug)
+    {
+        Pout<< "UPstream::reduce : value:" << Value << endl;
+    }
+
     if (!UPstream::parRun())
     {
         return;
@@ -433,11 +449,23 @@ void Foam::reduce(scalar& Value, const sumOp<scalar>& bop)
         }
         */
     }
+
+    if (Pstream::debug)
+    {
+        Pout<< "UPstream::reduce : reduced value:" << Value << endl;
+    }
 }
 
 
 void Foam::UPstream::waitRequests()
 {
+    if (debug)
+    {
+        Pout<< "UPstream::waitRequests : starting wait for "
+            << PstreamGlobals::outstandingRequests_.size()
+            << " outstanding requests." << endl;
+    }
+
     if (PstreamGlobals::outstandingRequests_.size())
     {
         if
@@ -458,11 +486,22 @@ void Foam::UPstream::waitRequests()
 
         PstreamGlobals::outstandingRequests_.clear();
     }
+
+    if (debug)
+    {
+        Pout<< "UPstream::waitRequests : finished wait." << endl;
+    }
 }
 
 
 bool Foam::UPstream::finishedRequest(const label i)
 {
+    if (debug)
+    {
+        Pout<< "UPstream::waitRequests : starting wait for request:" << i
+            << endl;
+    }
+
     if (i >= PstreamGlobals::outstandingRequests_.size())
     {
         FatalErrorIn
@@ -483,6 +522,12 @@ bool Foam::UPstream::finishedRequest(const label i)
         MPI_STATUS_IGNORE
     );
 
+    if (debug)
+    {
+        Pout<< "UPstream::waitRequests : finished wait for request:" << i
+            << endl;
+    }
+
     return flag != 0;
 }