The enzyme beta-glucuronidase (beta G) is shown, by histochemical methods, to be androgen inducible in the mouse epididymis. This trait has previously been believed to exist only in the kidney. Its presence in the genital tract constitutes a valuable tool in study of the developmental genetics of the reproductive system. Data presented here and previously imply co-ordinated genetic control of heterogeneous lysosomal populations. The results reported also provide a system for study of X-chromosomal activation, and of the developmental androgen dependence of the epididymis.