Psychosocial (sociodemographic characteristics, loss and separation and family atmosphere in childhood, recent life events) and biological (family history, DST, TRH-test) variables were investigated in 180 patients with Major Depression (MD) and Dysthymic Disorder (DD). The aim of the study was to reveal certain differences between the chronic and non-chronic course of MD and the early- and late-onset subtypes of dysthymia. When comparing the two course patterns of MD, a higher rate of malignant tumours among first-degree relatives, a greater number of long-lasting stress situations before the index depressive episode, longer duration of the previous episodes, less frequent DST nonsuppression, and a blunted TSH response to TRH were found in patients with a chronic course of MD. Several factors seem to influence the course pattern of MD, or else the chronic form represents a subgroup within MD. The late-onset dysthymics were mainly women with a low level of education, a lower suicidal tendency, normal suppression in DST, and a lack of blunted TSH responses to TRH administration during the period of double depression. The early-onset dysthymics showed a higher number of persons who had never married, who presented a more traumatic and frustrating childhood background, and who had a higher rate of DST non-suppressors and blunted TSH responses after TRH administration during the period of their double depression. Our data suggest that late-onset dysthymia might be a biologically distinct subgroup of chronic depression.