A study was conducted to compare the relative efficacy of fluoxetine and phenelzine in patients with mood-reactive atypical depression. Forty-two patients with atypical depression by the Columbia criteria were studied in a randomized, double-blind treatment study. Following a single-blind placebo lead-in, patients received fluoxetine 20-60 mg/day or phenelzine 45-90 mg/day for 6 weeks. Efficacy was measured by the Hamilton Depression Rating Scale, the Clinical Global Impression (Severity and Improvement) scales, and the Patient Global Impression (Improvement) scale. Of 42 patients randomized, 2 patients never received drugs and 2 phenelzine-treated patients dropped out prior to completion; the remainder completed the 6 weeks of the study. The rates of treatment response did not differ between groups. With a few exceptions (e.g., tremor), phenelzine produced more frequent adverse effects than fluoxetine. It was concluded that fluoxetine is as effective as phenelzine in the treatment of atypical depression, but produces fewer adverse effects and is better tolerated.