Ovarian volumes, measured with ultrasound, and serum estradiol and progesterone concentrations were studied during gonadotropin treatment cycles 1 week after hCG administration in 23 patients, of whom nine had polycystic ovarian syndrome (PCO), eight oligomenorrhea or amenorrhea corresponding to WHO group II (OMG), and six hypogonadotropic amenorrhea corresponding to WHO group I (HGT). The ovarian volumes were greater in the PCO and HGT groups than in the OMG group. The serum estradiol and progesterone concentrations correlated more closely with ovarian volumes in the HGT group than in the PCO and OMG groups. The present study failed to demonstrate a lower risk of hyperstimulation in the HGT group in comparison with the PCO and OMG groups. Six patients conceived, and ovarian volumes were greater and serum progesterone concentrations higher during conceptual cycles than during nonconceptual cycles.