Using the radioimmunoassay technique, we studied androgenic regulations of proteinase F in the submandibular salivary glands (SMG) of various mouse strains (ICR, BALB/CA, C3H/HeN, C57BL/ION, and DBA/2N). The proteinase contents in BALB/CA and DBA/2N mice were almost the same between males and females. However, prominent sex differences in enzyme content were seen in all other strains; i.e., male glands of C3H/HeN and C57BL/ l ON contained more proteinase F than female glands did. On the contrary, the enzyme level in the ICR was exceedingly higher in females than in males. The enzyme contents in ICR SMG increased in males following castration and decreased after androgen injection in both castrated males and normal females. On the contrary, the enzyme level in C3H/HeN was decreased by castration and increased by androgen injection. Therefore, these sex differences in ICR and C3H/HeN mice depend on androgen, though the direction of the response is opposite.