To examine antiestrogenic effects of danazol through the receptor system and to clarify its direct effects on the endometrium in vivo, we applied danazol jelly directly into the rabbit uterine cavity and measured uterine estrogen, progesterone and androgen receptors (ER, PR and AR, respectively). Danazol significantly reduced ER, PR and AR (p < 0.05). Treatment with receptor-blocking agents (RU 486 and oxendolone) showed that the decrease in the ER level showed a closer association with that in PR than with AR. These results indicate that danazol directly administered into the uterine cavity is absorbed by the endometrial tissue and exerts its antiestrogenic effects possibly through PR in the cells.