Androgens accelerated differentiation of human fetal urethral epithelial cells into secretory prostatic cells in organ culture. These epithelial cells contained supranuclear Golgi complexes in which acid phosphatase enzyme activity could be demonstrated by an electron microscopic histochemical technique. Most of the acid phosphatase activity was localized in lysosomes. Some apical precipitates could also be seen. This apical activity might be in secretory granules. Also, mesenchymal cells contained this enzyme.