[snip my struggle with ZClasses that derive from Python base classes inside ZClasses] Okay, this *still* didn't work; apparently the ObjectManager ZClass was somehow put into a wrong state -- even if I deleted the old field ZClasses (for instance IntegerField), it would still show up in the add list -- probably because it could find an IntegerField Python base class? Anyway, I created a while new ObjectManager ZClass, created a while new Field class inside, and now it seems to work properly. I hope this kind of ZClass weirdness is fixed in the CVS version of Zope; if not read my mails for the symptoms. It can get very confusing and frustrating. But-I-suppose-I'm-the-only-guy-deriving-ZClasses-from-his-Python-base-classes-ly yours, Regards, Martijn