OBJECTIVE: To study the effectiveness of fluoxetine and cognitive-behavioural counselling in depressive illness in postnatal women: to compare fluoxetine and placebo, six sessions and one session of counselling, and combinations of drugs and counselling. DESIGN: Randomised, controlled treatment trial, double blind in relation to drug treatment, with four treatment cells: fluoxetine or placebo plus one or six sessions of counselling. SUBJECTS: 87 women satisfying criteria for depressive illness 6-8 weeks after childbirth, 61 (70%) of whom completed 12 weeks of treatment. SETTING: Community based study in south Manchester. MAIN OUTCOME MEASURES: Psychiatric morbidity after 1, 4, and 12 weeks, measured as mean scores and 95% confidence limits on the revised clinical interview schedule, the Edinburgh postnatal depression scale and the Hamilton depression scale. RESULTS: Highly significant improvement was seen in all four treatment groups. The improvement in subjects receiving fluoxetine was significantly greater than in those receiving placebo. The improvement after six sessions of counselling was significantly greater than after a single session. Interaction between counselling and fluoxetine was not statistically significant. These differences were evident after one week, and improvement in all groups was complete after four weeks. CONCLUSIONS: Both fluoxetine and cognitive-behavioural counselling given as a course of therapy are effective treatments for non-psychotic depression in postnatal women. After an initial session of counselling, additional benefit results from either fluoxetine or further counselling but there seems to be no advantage in receiving both. The choice of treatment may therefore be made by the women themselves.