In order to evaluate the effect of immobilization during bed rest on mental health, we performed psychosomatic investigations of 6 young males and 3 young females before, during and after 20 days bed rest. The psychological state was repeatedly assessed by measuring the following indices: 1) Zung's self-rating depression scale, 2) Cornell medical index, and 3) the General Health Questionnaire. Zung's self-rating depression scale is a measure of the state of depression, while Cornell medical index and the General Health Questionnaire are utilized for detection of neurosis. Although no influence of bedrest on Cornell medical index was seen, Zung's self-rating depression scale and the General Health Questionnaire displayed a tendency to development of depression and neuroses, respectively. This tendency had disappeared 2 months after the bed rest study. Both Zung's self-rating depression scale and the General Health Questionnaire may be appropriate indices to evaluate the effects of relatively short-term psychological stress due to bed rest. The urinary excretion of 17-hydroxycorticosteroid was used as an indicator of endocrine stress factors, but no significant variation due to bed rest was seen. We concluded that there is a need for further studies combining physiological research with psychosomatic investigations.