The Unified Modeling Language provides two complementary notations, state machines and collaborations, for the specification of dynamic system behavior. We describe a prototype tool, HUGO, that is designed to automatically verify whether the interactions expressed by a collaboration can indeed be realized by a set of state machines. We compile state machines into a PROMELA model and collaborations into sets of Büchi automata (“never claims”). The model checker SPIN is called upon to verify the model against the automata.