The uptake and metabolism of [1,2-3H]dihydrotestosterone and [1,2-3H]-testosterone by explants of rat ventral prostate maintained in organ culture have been assessed under circumstances in which constant intracellular levels of the hormones have been achieved. Dihydrotestosterone was the principal intracellular androgen whether the hormone in the incubation medium was testosterone or dihydrotestosterone, and intracellular to extracellular gradients for dihydrotestosterone were greater than those for testosterone under all conditions studied. These findings are compatible with the possibility that the conversion of testosterone to dihydrotestosterone and the subsequent binding of dihydrotestosterone to receptor sites within the tissue serve to keep the activity of intracellular testosterone low and to promote passive diffusion down an activity gradient from blood. The net effect of such a system is the development in the prostate of a higher concentration of total androgen (testosterone plus dihydrotestosterone) than in the medium.