It has been well known that the fasting therapy which was invented in Medical School of Tohoku University reveals an excellent effect upon various kinds of psychosomatic diseases, but its therapeutic mechanism and suitable indication are not yet explained completely. In order to corroborate these problems, this study was undertaken on 262 cases of psychosomatic diseases in the field of internal medicine. It is a complete fasting for 10 days with nothing by mouth except for drinking water, and 500 ml of parenteral fluid containing vitamins are administered intravenously every day. Absolute bed rest and self meditation are required in a closed individual room, and patients are not allowed to meet anyone but physicians and nurse in charge. The return to normal ordinary diet follows the order of fluid diet, soft diet and semiordinary diet during 5 days. In the period of the therapy, various clinical and laboratory examinations were carried out. Significance of these examinations consists in prediction of possible danger during the fasting period and elucidation of its therapeutic mechanism. Consequently, an outstanding efficacy rate of 87% with excellent prognosis was attained, and the following diseases were determined as suitable indication of this therapy; irritable colon, dysorexia nervosa, borderline hypertension, neurocirculatory asthenia, bronchial asthma, mild diabetes mellitus, obesity, lumbago without organic findings, conversion hysteria, various neurosis with somatic symptoms and masked depression. Possible mechanism of action of the therapy is that fasting acts as an extreme stress on the function of the autonomic nervous and endocrine systems, then it regulates the function of whole body including the brain, also it acts as one of the behaviour therapy for abnormal conditioning.