The following results were obtained from our investigations performed to compare the effects of danazol (400 mg/day orally for 4 to 6 months, n = 164) with those of buserelin (900 micrograms/day intranasally for 4 to 6 months, n = 83) on patients with uterine myomas. The effectiveness of buserelin (76.1%) in shrinking uterine myomas was better than that of danazol (56.7%). The serum-estradiol and progesterone levels were lower in the buserelin group than in the danazol group. The estrogen and progesterone receptors in a hysterectomied uterus were positively stained even at the end of those therapies. The degree and frequency of hyaline degeneration were higher in the buserelin group than in the danazol group. Thus, the shrinking of uterine myomas and the degree of hyaline degeneration might be caused by the lowering of uterine-tissue hormones, particularly of estradiol levels.