Serum levels of testosterone, androstenedione and dehydroepiandrosterone were measured before and after 5 days of treatment with hCG (2000 IU/d) in 36 prepubertal boys with cryptorchidism and 11 with hypospadias in order to determine whether a defect in androgen synthesis could be a common cause for these disorders. Baseline and stimulated levels of testosterone, androstenedione and dehydroepiandrosterone were similar in patients with unilateral cryptorchidism, monorchism and hypospadias; baseline and stimulated levels of testosterone were lower in boys with bilateral cryptorchidism. Testosterone levels did not correlate with either the anatomical location of the testis in patients with unilateral cryptorchidism or with the site of the urethra in boys with hypospadias. Seven of 36 patients with cryptorchidism had a positive family history of a similar disorder; testosterone levels were similar in patients with and without a family history. It is concluded: 1) in all patients studied, the gonadotropin dependent phase of testosterone production is present; 2) hCG stimulation cannot detect unilateral Leydig cell dysfunction; and 3) in familial cases of cryptorchidism, some factor other than an abnormality in androgen synthesis may be responsible for the hereditary tendency.