Estrogens (estrone [E1] and estradiol [E2]), their sulfates and progesterone receptor (PR) were evaluated in patients with uterine leiomyomata nontreated and treated with Decapeptyl (D-Trp6-gonadotropin-releasing hormone [GnRH]; Ipsen Biotech, Paris, France). Estrogen concentrations are very high in the leiomyoma (secretory phase, pg/g tissue [mean +/- SEM]: n = 10; E1: 147 +/- 24; E2: 850 +/- 116; E1-sulfate: 1,668 +/- 808; E2-sulfate: 718 +/- 126). Decapeptyl treatment provokes a significant decrease in E2 and particularly in E1 and E2 sulfates. Progesterone receptors were higher in the leiomyoma than in the myometrium; after a long treatment (3 to 4 months) a significant decrease in both tissues is observed. The decrease provoked by D-Trp6-GnRH on estrogens (unconjugated and sulfates) and in PR in the leiomyoma after long treatment, supports the hypothesis that estrogens are implicated in the cause of these tumors.