Suppression of the secretion of gonadal steroids by chronic administration of a superactive agonist of luteinizing hormone-releasing hormone (LH-RH) was used for treatment of leiomyomata uteri. Ten menstruating women, presenting with a total of 20 uterine leiomyomas, were treated for 3 months with daily subcutaneous injections of D-Trp6-LH-RH. Serum estradiol (E2) levels were suppressed rapidly in five patients and were decreased in other patients. At the end of therapy, leiomyomas regressed completely in three patients, while five patients showed a decrease of more than 40% in the volume of leiomyomas. The reduction in tumor size was correlated with the rapidity of the fall in serum E2 levels. In one patient, the leiomyomata increased in size during treatment, and one woman had a poor clinical response. The agonist was well tolerated and few side effects were observed. Therapy with LH-RH agonists offers an alternative in the management of some uterine leiomyomas.