Of more than 500 boys with bilateral cryptorchidism who presented during a 10-year period 28 prepubertal patients less than 11 years old who had no palpable testes after human chorionic gonadotropin therapy were studied to assess the ability of serum gonadotropin levels to identify patients with anorchism. Of the boys 21 had a normal testosterone response to human chorionic gonadotropin therapy and all of them had testes at exploration. The serum luteinizing hormone levels ranged from 2 to 6 mIU per ml., with a mean of 3.7 mIU per ml., and the serum follicle-stimulating hormone levels ranged from 1.6 to 6.2 mIU per ml., with a mean of 3.7 mIU per ml. Seven patients showed no testosterone response to human chorionic gonadotropin and all but 1 underwent exploration, at which time no testes were found. Of these 7 patients 6 had elevated gonadotropin levels that averaged 3 standard deviations above the mean. For comparison, 2 pubertal patients with nonpalpable gonads and 3 castrated prepubertal boys also were studied. From the study we concluded that in boys with nonpalpable gonads 1) abnormally elevated serum gonadotropin levels before puberty are indicative of anorchism, 2) neither exploration nor human chorionic gonadotropin stimulation tests are essential for diagnosis in these select patients, 3) serum gonadotropin levels alone are not sufficient for a definitive diagnosis after puberty and 4) all boys with normal serum gonadotropin levels must undergo exploration regardless of the outcome of a human chorionic gonadotropin stimulation test.