If a message is discarded while an user routine is processing that same message, the system rejects subsequent attempts by the user routine to process the message with a return and reason code indicating that the message has been discarded. Depending on the timing, the current operation being performed by the user routine might be allowed to complete before the message is discarded. The system returns from the IXCMSGC Discard Message service with the discard of the message left pending.