It's possible thread scheduling is coming into play (runnining on WinXP), but I think some of my experiments indicate something else is having an effect. By way of background, the app uses CMP EJB 2 beans and is deployed under JBoss 4.0.4, UIL2, and JDK 1.6. UI is JSF/MyFaces and DB is MySQL 5.0.18. The queue is the default configuration queue A. The intent is to send messages from the UI thread to an analysis queue MDB without waiting for the results. Tried adding a sleep() as suggested to the MDB (there was already a yield() there). Still acted synchronous. Modified the sender to spawn a low priority thread to perform the send (I know, bad EJB practice). Still synch. Created a standalone sender from the JBoss examples sending to the app. Acted asynch - the sender posted the messages without waiting for the MDB to process them. Ran a standalone receiver with simulated load and app sending. Acted asynch, sender posted messages without waiting. Reverted to app sending and receiving. Still synch, with or without transacted messages. So it appears something is going on when the app UI thread is sending to the MDB. They are entirely separate thread groups (main vs. RMI Runtime), so it's not clear to me where the scheduling issue is arising. Might it have something to do with CMP? Something else? Thanks. Bob View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4046941#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...