Endocrine studies were carried out on 3 patients with streak gonad syndrome, 2 of whom had slight proliferative vaginal smear patterns, and the 3rd had slight hirsutism with increased muscle mass but an atrophic type vaginal smear pattern. Simultaneous sampling of peripheral, adrenal and streak gonadal venous blood revealed mildly increased testosterone secretion by the streaks in the 2 patients who had proliferative cytohormonal patterns. Histologic examination of their streak gonads showed hilus cell hyperplasia. It might be suggested that hilus cell hyperplasia was the source of the increased testosterone secretion in these 2 patients and thus resulted in slight maturation of the vaginal epithelium.