To effectively uncover aspect defects, system (or subsystem) testing is of importance because aspects crosscut multiple system components. This paper presents an approach for generating system test requirements from aspect-oriented use cases. Central to this approach is the formalization of a testable system model from aspect-oriented use cases. We explicitly capture various constraints among base and aspectual use cases. Specifically, we transform aspect-oriented use case diagrams and descriptions into aspect-oriented Petri nets. This makes it possible to generate meaningful use case sequences with respect to various coverage criteria (such as use case coverage, transition coverage and state coverage). When scenario tests for individual use cases are available, they can be composed into system tests according to the generated use case sequences. Copyright 2007 ACM.