To evaluate the role of maladaptive thinking patterns in depression, the authors administered the Dysfunctional Attitude Scale to 112 depressed patients before and after 3-6 weeks of treatment with antidepressants or placebo. Twenty-two normal subjects were also assessed twice. Depressed patients had a significantly higher initial mean score than control subjects, but during treatment their score significantly decreased, and the posttreatment score of those with complete recoveries was nearly as low as the control subjects' final score. The higher the initial dysfunctional attitude score the poorer the response to treatment. Patients with endogenous depression had significantly lower scores than nonendogenously depressed patients.