Objectives: The effects of a stress reduction program on Japanese blue-collar workers were investigated using a controlled trial design. Methods: Two blue-collar worksites that showed higher depression scores (Zung self-rating depression score) were selected for the intervention group, after a survey of a large electric company in 1985. Three blue-collar worksites were selected as a reference group whose workers were matched with the workers of the interventive worksites by mean age, worksite size and mean depression scores. A 1-year stress reduction program was conducted in the intervention group from 1986 to 1987 by worksite supervisors. Effects of the stress reduction program were assessed by comparing the initial depression scores, length of sick leave, and systolic and diastolic blood pressures with those after the follow-up. Results: The depression scores decreased during the follow-up in the intervention group, while the scores were almost the same in the reference group. An analysis of covariance with repeated measurements indicated a statistically significant intervention (group x time interaction) effect after control for gender and age (P = 0.035). Sick leave in the past year decreased in 1988 only in the intervention group; generalized logit analysis with repeated measurements indicated a statistically significant intervention effect after control for gender and age (P = 0.034). No statistically significant intervention effects were observed on systolic and diastolic blood pressures or selected work stressors. Conclusions: A stress reduction program directed towards worksite supervisors can be used to reduce depressive symptoms and sick leave among Japanese blue-collar workers.