The Sertoli cell appears to be a target cell for both FSH and androgen. FSH stimulates the Sertoli cell to produce an androgen-binding protein (ABP) which may serve to increase the accumulation of androgen in the seminiferous tubular epithelium and make it available for binding by intracellular androgen receptors. This might be one way by which FSH enhances the action of androgen on spermatogenesis. Androgen acts on the Sertoli cell to increase its response to FSH resulting in increased production of ABP and of other substances which exert trophic effects on spermatogenesis.