To examine the relationship between psychosocial job stress and major depression, a prospective cohort study was conducted of 3066 male workers in two factories of an electrical company in Japan. The workers were observed for 3 years; 15 workers newly developed major depression. The effects of six job stress variables, depressive symptoms, and other possible confounders were assessed by means of self-administered questionnaires once a year. Five workers without apparent psychiatric disorder were matched for each patient by gender (all male), age (within 5 years), marital status, factory, and occupation; the 15 cases and the 75 controls were compared. Proportions of perceived stress due to unsuitable jobs and human relations were significantly higher in the cases than in the controls. Results of the conditional multiple logistic regression analysis indicated that stress due to unsuitable jobs was significantly associated with occurrence of major depression after depressive symptoms were controlled for. It is suggested that stress due to unsuitable jobs is a possible risk factor for major depression in industry.