Non-verbal behaviour of 22 unipolar, non-delusional depressed outpatients was video-recorded during psychiatric interview to determine whether response to tricyclic treatment (50-100 mg/day of amitriptyline for 5 consecutive weeks) could be predicted on the basis of the ethological profile at baseline. At the end of the study, patients were divided into two treatment outcome groups on the basis of their final Hamilton Depression Rating Scale (HDRS) scores. At baseline, responders (n = 14, HDRS score less than or equal to 10) and non-responders (n = 8, HDRS score greater than 10) did not differ with respect to sex, age, education, DSM-III diagnosis, and HDRS score. In contrast, ethological profiles of the two treatment outcome groups at baseline were different, with non-responders showing significantly more assertive and affiliative behaviours. The results are discussed in the light of previous studies which have identified subgroups of depressive patients with different responsiveness to tricyclic treatment.