Pharmacokinetic can perhaps explain that about 30% of depressed patients do not respond to tricyclic antidepressants. Studies of the relationship between the pharmacokinetic and pharmacological effects of the tricyclic antidepressants are particularly important. Clomipramine is a tricyclic antidepressant widely used. But there are disparities in various findings on relationship between plasma levels of this drug and clinical effect. Forty in-patients, with an endogenous or exogenous depressive syndrome, received clomipramine orally. In 19 patients treated by 75 mg per day of clomipramine, there was a great interindividual variability of the plasma levels at the 28 day treatment. A comparison of clinical response with plasma levels of clomipramine and desmethylclomipramine, showed a significant negative linear correlation at day 28.