After a nine-day control period, six hospitalized obese women were placed on 500 calorie diets and were given 125 IU of human chorionic gonadotropin (HCG) intramuscularly daily for 30 days. Another five obese women received injections of diluent only and consumed identical diets for the same period. Mean weight loss in the HCG-treated group was nearly identical to that achieved by women given the placebo. Reduction of triceps skinfold thickness or circumferential body measurements of the chest, waist, hips, and thighs were not different. Patters of change of a variety of plasma and urine substrates, electrolytes, and hormones were similar in the two groups and consistent with semistarvation and weight loss. These results indicate that HCG has no effects on chemical and hormonal parameters measured and offers no advantage over calorie restriction in promoting weight loss.