Mice with mosaic mutation could be one of the models of human Menkes disease, which is associated with abnormal cooper metabolism. The aim of the present study was to localize androgen receptors (ARs) in the testes by means of immunohistochemistry. AR expression was observed in the nuclei of all somatic cells such as Leydig cells, Sertoli cells, and peritubular cells in sections from testes of control and mosaic mutant males. In the latter, very strong immunoreactivity for AR as well as higher levels of steroid hormones in homogenates were noticed in comparison to control mice. No positive immunoreaction for ARs was seen in control sections incubated without the primary antibody.