Seventy-four patients who met DSM-III criteria for social phobia completed 8 weeks of double-blind, randomly assigned treatment with the monoamine oxidase inhibitor phenelzine sulfate, the cardioselective β-adrenergic blocker atenolol, or placebo. The overall response rates were 64% for phenelzine, 30% for atenolol, and 23% for placebo. Phenelzine was widely superior to both atenolol and placebo on independent rater analyses and, to a lesser extent, on self-report, with no significant differences between atenolol and placebo. At the end of 16 weeks, phenelzine was still significantly superior to placebo, while atenolol showed an intermediate response that did not differ significantly from either of the other treatments. Patients with generalized social phobia constituted 76% of the sample, and they were preferentially responsive to phenelzine. The small size of the discrete social phobic sample precluded separate outcome analyses for this subtype. Overall, the findings support the responsivity of social phobia to monoamine oxidase inhibitors.