Hello, I am trying to find out what should happen, according to the MPI 3.0* standard, in the following scenario: 1) process 0 initiates a nonblocking send operation with MPI_Issend 2) process 1 matches the message with MPI_Mprobe, but doesn't yet call MPI_ Mrecv/MPI_Imrecv 3) process 0 calls MPI_Cancel to cancel the send. I cannot think of anything the cancel operation could do that wouldn't contradict either the specification of MPI_Cancel, or of the matched receive functions. How can this situation be handled in compliance with the standard? Thank you in advance, Marek Tomáštík *or 3.1 -- I believe there weren't any changes in this area?