The effect of chronic treatment with amineptine (200 mg daily), a tricyclic antidepressant drug selectively blocking dopamine uptake, on 3H-imipramine binding, was investigated in platelets of major depressed patients in conjunction with changes in clinical state. Before treatment, depressed patients had a significantly lower Bmax (P less than 0.01) than age- and gender-matched healthy controls. After only 1 week of amineptine administration, Bmax values increased significantly (P less than 0.01) and reached the control value concomitantly with a large and significant clinical improvement (P less than 0.01). After 1 month, Bmax was still significantly different from the pretreatment value (P less than 0.05), and not significantly different from the control value, while the improvement in clinical status persisted. No significant changes in Kd values were observed during treatment. We also verified that amineptine did not displace 3H-imipramine binding from platelets either in depressed or in control subjects. The results show that the successful treatment with amineptine, an antidepressant drug devoid of affinity for the tritiated imipramine platelet binding site, can rapidly lead to its density normalization.