Peter is right, though for the wrong reason. :) SLSBs *do* have state, as the instance is returned to the Pool after use. Therefore invocation-specific data should not be kept in instance members of a SLSB. For SFSB this is acceptable (and good practice) because it's guaranteed that every subsequent invocation upon a given proxy will invoke upon the same SFSB instance. However, EJBs are Thread-safe - no two invocations will use the same instance concurrently (by spec anyway): "EJB 3.0 Core Specification 4.7.11" wrote : The container must ensure that only one thread can be executing an instance at any time. S, ALR View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4171100#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...