Abstract. Action refinement in process algebras has been widely studied in the last few years as a means to support top-down design of systems. A specific notion of refinement arises when a dependency relation on the actions (in the Mazurkiewicz sense) is used to control the inherf orderings from the abstract level. In this paper we present a rather simple operational semantics for dependency-based action refinement. We show the consistency of the operational with a (previously published) denotational semantics. We moreover show that bisimulation is a congruence for dependency-based refinement. Finally, we give an illustrative example.