Seventy-four patients meeting DSM-III criteria for social phobia completed 4 or more weeks of double-blind, randomized treatment with the monoamine oxidase inhibitor phenelzine, the cardioselective beta-adrenergic blocker atenolol, or placebo. Sixty-four percent of the patients on phenelzine demonstrated moderate or marked improvement, compared to 30 percent on atenolol and 23 percent on placebo. Phenelzine was significantly more effective than atenolol or placebo, whereas the efficacy of atenolol and placebo did not differ significantly. Patients were also prospectively divided into generalized and discrete subtypes of social phobia. Phenelzine appeared to be a particularly effective treatment for the generalized form of social phobia. Atenolol may be useful for discrete forms of social phobia such as performance anxiety.