The selective serotonin reuptake inhibitor citalopram was compared with clomipramine in a multicenter clinical study. From a total of 150 depressed patients (age 18-65 years), 114 patients with a Hamilton Depression Scale (HDS) total score greater than or equal to 18 at the end of a 1 week placebo period were started on treatment with either citalopram (40 mg/day) or clomipramine (150 mg/day) (fixed, single daily dose). Patients stratified according to diagnostic rating (Newcastle Inventory, endogenous/non-endogenous) were randomly allocated to treatment groups using double blind principles. In total, 102 patients completed more than 2 weeks, treatment and were included in the analyses of therapeutic effect. The two drug groups were comparable in terms of sex, age, and departmental distribution. Categorical measurements of therapeutic effect based on the HDS total score showed that in the endogenously depressed patients a significantly higher percentage of patients on clomipramine (n = 37) than on citalopram (n = 38) were classified as complete responders (HDS total less than or equal to 7) after 3, 4 and 5 weeks of treatment. In the non-endogenously depressed patients (clomipramine: n = 15, citalopram: n = 12) rather similar numerical differences were observed (P less than 0.05 at 5th week). In the total patient group the percentage of complete response after 5 weeks was about 60 in the clomipramine group (n = 52) and about 30 in the citalopram group (n = 50) (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)