Earlier studies showed a sex dimorphism of the adrenal cortex of the hamster developing during puberty. Morphologically, this is most evident in the zone reticularis. The male has larger reticular cells than the female, 60 pairs of siblings were castrated around the 10th day of life; 6 males and females were sacrificed at weekly intervals between the 3rd and 12th week of life. 60 pairs of uncastrated siblings served as control. Till the 10th week of life the body and adrenal weight of the castrated males agree with those of the castrated females. From the 11th week onwards the males have the higher body and adrenal weight. Neither histometrically nor histologically there are differences in the adrenal structure of the 2 castrated sexes. Both groups have small reticular cells. Compared to the uncastrated animal the male castrated hamster has a higher body and a lower adrenal weight, whereas the female castrate shows no significant difference in comparison with the non-castrate of the same age and sex. Thus, the adrenal cortex of the Syrian golden hamster is stimulated by androgen hormone. This result is contrary to the rat adrenal, where changes, caused by gonadectomy, are found in the female, and the female adrenal is stimulated by estrogen.