Testosterone propionate accelerates the maturation of acinar cells in the preputial gland of female rats. The weight of the preputial gland was increased significantly and the gland contained a large amount of secretory material. Various stages of maturation of acinar cells were observed. In an early stage, cells contained predominantly rough endoplasmic reticulum. In a second stage, lipid accumulated in association with focal areas of smooth endoplasmic reticulum. Membrane-bound dense bodies similar to lysosomes and secondary lysosomes predominated in a late stage. In the final stage, acini fused with a duct, thereby liberating the cells into the ductal lumen. Cell structure then became unrecognizable.