Following incubation of rat ventral prostate homogenates with 1,2-3H]-5α-dihydrotestosterone, the steroid was taken up and bound by the nuclei. Sodium chloride extraction of the nuclei removed macromolecules which might at least be partially responsible for the binding. Purified nuclei which were incubated with the radioactive steroid in either Tris-EDTA buffer or a 105 000 × g supernatant fraction prepared from the organ showed a lower degree of binding. Gel filtration chromatography of sodium chloride extracts from these nuclei disclosed binding of steroids to macromolecules. In all the experiments the steroids bound by nuclei consisted of unchanged 5α-dihydrotestosterone.