The DNA content of spermatogonia was studied by cytophotometric quantification in the testes of cryptorchid children and adults, as well as in age-matched control males. In most cases, the average DNA content of spermatogonia was significantly increased in the cryptorchid testes of children with uni- or bilateral cryptorchidism, as well as in the contralateral scrotal testes of children with unilateral cryptorchidism. In the group of adult men the average DNA content of spermatogonia in the testes was even more increased than in children. There were not significant differences between 4 and 14 years of age, between unilateral and bilateral cryptorchidism, or between cryptorchid testes and contralateral normally descended testes. The DNA content of spermatogonia in the surgically descended testes of 3 children who were re-biopsied 3-4 years after orchidopexy was similar before and after orchidopexy. These findings suggest that the spermatogonia of many cryptorchid males bear a congenital lesion.