The pituitary-gonadal axis was studied in 28 men with severe protein-calorie malnutrition in a Calcutta hospital. The men were selected for the severity of their malnutrition and for absence of other diseases. They had clinical findings of hypogonadism and low total and unbound plasma testosterone. During 2-5 months of refeeding there was clinical recovery and increase of plasma testosterone to normal. Plasma LH was high in malnutrition, decreased during refeeding, and remained above normal after refeeding. Some patients failed to show LH elevation in malnutrition despite low plasma tesosterone. Plasma FSH was high in malnutrition, decreased during refeeding, and was near the level of normal Indian men after refeeding. HCG 4000 IU im per day for 3 days produced subnormal increments in plasma testosterone both in malnutrition and after refeeding; corresponding decreases in FSH occurred. It is concluded that the hypogonadism of protein-calorie malnutrition is primarily on the basis of diminished Leydig cell function. Appropriate pituitary LH response is intact in some patients, but is either absent or inadequate in others. Subclinical Leydig cell insufficiency, indicated by LH elevation and subnormal response to HCG, persists after refeeding has produced recovery from malnutrition and clinical hypogonadism. FSH elevation in malnutrition may be secondary to the reduced Leydig cell function.