In preliminary attempts to find a technique for internal irradiation of the prostate, studies using regional perfusion of the dog's prostate with P/sup 32/ compounds showed that the prostate received higher concentrations of the isotope than other viscera. Whether the isotope was deposited intraepithelially or was present only in the extracellular fluid was investigated by microradioautography. Two compounds containing P/sup 32/, sodium phosphate and diethylstilbestrol diphosphate, were used. Four methods for introducing P/sup 32/ into the epithelial cells of the dog's prostate are described: intravenous injection, intraarterial infusion, regional perfusion, and retrograde injection via the urethra. Intraepithelial localization of both P/sup 32/-labeled compounds was demonstrable in microradioautographs of prostate, especially when urethral injections were made. The radioactivity of prostate was approximates 400 times higher by this route compared with the other 3 when measurements were made 24 hr postinjection. (TCO)