A low protein, but calorically unrestricted, diet was used to treat 42 overweight patients. The immediate results were encouraging: 32 subjects lost 100 or more grams per day, and continued to feel well. After they were discharged, however, a majority of patients returned to their previous ways of eating. At follow-up examinations 3 to 12 months after discharge, it was found that 52 per cent of the patients had regained all of their original weight, 30 per cent had remained nearly steady, and 18 per cent had continued to reduce without supervision. Prescription of a high protein supplement led to an increase in the voluntary consumption ofunprescribed calories, thus suggesting that the limitation of protein to 35 ± 5 Gm/day actually had reduced appetite. In addition, the results indicated that the routine of treatment (scheduling of meals, restriction in choice of food, regulation of activities) contributed significantly to the control of appetite. The general health remained good, and liver function, as studied by serial tests, remained unchanged by treatment. Limitation of protein appears to be a useful adjunct to the treatment of obesity; but, as with any other diet, regular medical supervision is essential. It offers a means of regulating appetite during the maintenance period that follows any successful course of reduction, and suffices as a sole measure of treatment for milder degrees of overweight.