Hello Florent and Dieter, Thanks for the reference to showaq and the test case. The test case provided by Florent works well on 2.4.0. also which forced me to refine my problem. Only python scripts and external methods where used instead of zsql object to simplify the latest test. The following fails when I pass a parameter to the external method with the message Error Type: AttributeError Error Value: util File Zope-2.4.0/Extensions/ex_test.py, line 2, in ex_test The invocation URL is http://localhost:8080/test/dev/alpha/py_alpha The sequence should be py_alpha -> py_beta -> ex_test -> py_delta. /test/util/ex_test #external method calling a python script def ex_test(self,param=''): return ' ex_test ' + self.util.py_delta() /test/util/py_delta #python script return ' delta ' /test/dev/alpha/py_alpha #python script calling a python script return ' py_alpha ' + context.beta.py_beta() /test/dev/master/beta/py_beta #python script calling an external method return ' py_beta ' + context.util.ex_test('boing') However changing the contents of py_beta to return ' py_beta ' + context.util.ex_test() succeeds returning "alpha beta ex_test gamma" as expected. Note the absence of a parameter passed to external method ex_test from py_beta. Is there something I'm missing? Thanks, Jelle