A theory of communication between autonomous agents should make testable predictions about which communicative behaviors are collaborative, and provide a framework for determining the features of a communicative situation that affect whether a behavior is collaborative. The results presented here are derived from a two-phase empirical method. First, we analyze a corpus of naturally-occurring problem-solving dialogues in or- (ler to identify potentially collaborative communicative strategies. Second, we experimentally test hyl)otheses that arise from the corpus analysis in Design-World, an experimental environment for simulating dialogues. The results indicate that collaborative behaviors must be defined relative to the cognitive limitations of the agents and the cognitive demands of the ta~sk. The method of computational simulation provides an additional empirical basis for theories of collaborative discourse.