You try to make all nontransient variables, which are not one of the following to null. For the given list the container takes care of serializing and restoring the object when activated. Serializable objects, null, UserTransaction, SessionContext, JNDI contexts in the beans context, reference to other beans, references to connection pools. Things that must be handled explicitly are like a open database connection etc. These must be closed and set to null and retrieved back in the activate method.