Total fast periods of 4 to 14 days in the management of 50 cases of intractable obesity achieved a prompt decrease in body weight of approximately 2.5 lb. per day. Subsequent shorter fast periods served to prevent a recurrence of the obese state and, also, to achieve further reduction in weight in the ensuing weeks. Non-nutritious fluids were allowed ad libitum and polyvitamins were given. Exercise was interdicted. Anorexia was the rule after the first day of fasting and paralleled the degree of hyperketonemia. A sense of well-being was associated with the fast. The patient's subsequent 1- or 2-day fasts, as an outpatient promoted his reassurance that he had within his grasp a means of effectively combating what had formerly appeared to be a hopeless situation.