Symptom reduction and improvement in functioning in women with postpartum major depression treated with a tricyclic antidepressant versus a serotonin reuptake inhibitor were compared. The design was a double-blind, 8-week comparative trial of nortriptyline (NTP) versus sertraline (SERT) with a 16-week continuation phase. Women aged 18 to 45 years with postpartum major depression and a 17-item Hamilton Rating Scale for Depression score of 18 or more were eligible. Subjects were randomized to NTP or SERT and treated with a fixed-dosing strategy. Of 420 women interviewed, 109 eligible women received medication, and 95 provided follow-up data. The proportion of women who responded and remitted did not differ between drugs at 4, 8, or 24 weeks. Times to response and remission also did not differ. Psychosocial functioning improved similarly in both drug-treated groups of mothers. The total side effect burden of each drug was similar, although side effect profiles differed between agents. No clinical or demographic variables differentiated responders by drug. Women who were responders and remitters at week 8 could be identified earlier if they were treated with SERT than with NTP. Breast-fed infant serum levels were near or below the level of quantifiability for both agents.