This study sought to test hypotheses derived from Trower and Gilbert's (1989) psychobiological/ ethological model of social anxiety. This model purports that social anxiety should be characterized by less social cooperation and dominance and greater submission and escape/avoidance. Individuals with social phobia and nonanxious participants completed a structured social interaction. Behavioral measures related to cooperativeness, dominance, submissiveness, and escape/avoidance were coded by independent observers. Those with social phobia exhibited fewer behaviors of social cooperativeness and dominance than did nonanxious participants. The groups did not differ with regard to submissive and escape/avoidance behaviors. Two dominance behaviors correlated with a self-report measure of social anxiety. Implications for the Trower and Gilbert model and for social anxiety theory and treatment are discussed. Social phobia is an excessive fear of social situations in which the person anticipates scrutiny from others, resulting in irrational expectations of humiliation and embarrassment. People with social phobia fear various situations, including conversing, drinking, eating, public speaking, and being observed by others (American Psychiatric Association, 1994). It has become generally accepted that social phobia affects a significant portion of the population-approximately 13% at some time during the lifespan (Kessler et al., 1994). Onset