Ten patients who suffered from a primary depressive illness were treated with a new antidepressant drug butriptyline (150 mg/day). Six of the patients showed marked clinical improvement, as judged by depression rating scores, at the end of 22 days of treatment. No simple relationship was found between clinical response and plasma butriptyline concentration. Butriptyline is an effective antidepressant agent, well tolerated and with few side effects.