Hi Paul I'm writing because I had the same trouble that you describe on this page: http://www.zope.org/Members/paulabrams/howto_deleteundeadzclassprops For the sake of the list, I quote: I noticed that when you delete a property in a ZClass, it doesn't actually delete the property in instances of that ZClass! This leaves zombie properties lying around where they can be inadvertently acquired, causing problems that are difficult to trace. Since these properties override properties set in the REQUEST, if the do get acquired they are difficult to override. I logged this bug in the collector, which affected my Zope 2.1.6 install. Maik Röder was kind enough to email me the solution below. He solved the problem by adding this External Method, and calling all instances with it:: #move_attribute?the_id=abstract def delete_attribute(self,the_id): self._delOb(the_id) On Zope 2.3.3, this gets me:: Error Type: AttributeError Error Value: _delOb I tried 'manage_delObjects(ids)' and 'manage_delProperties(ids)', without success. I'd like to ask whether you've learnt anything new about this problem since 2000/12/05? Also, could you tell me what the Issue Id of this issue is in the collector? I tried searching at http://classic.zope.org:8080/Collector/ but without success. Regards, Jean Jordaan