BOMT has been found to suppress nuclear binding of DHT in prostate gland in vitro and to compete with DHT for the specific high-affinity binding sites for DHT in the prostate cytoplasm. BOMT reduces the transfer of DHT into prostate chromatin in a reconstituted cell free system and antagonises the stimulation by testosterone of prostate RNA polymerase activity on injection in vivo. owever BOMT was found to have no effect on the 5α-reductase activity of rat prostate minces in vitro. It is suggested that the anti-androgenic properties of BOMT on the rat prostate gland can be explained by its competition for DHT binding sites within the gland.