Intermittent sc injection of a LHRH agonist reduced uterine fibroid size in 5 women. Commencement of the LHRH agonist buserelin on day 21 of the menstrual cycle induced a marked increase in plasma LH and FSH concentrations, followed by rises in estradiol (E2) and progesterone. LH and FSH levels fell to within the normal range by 120 h after beginning buserelin, despite continuing administration of the agonist. After menstruation, marked sustained suppression of cyclical gonadotropin and steroid concentrations occurred: mean values of FSH, LH, and E2 were 4.9 +/- 0.5 (+/- SE) mIU/ml, 5.9 +/- 0.6 mIU/ml, and 47.9 +/- 10.8 pg/ml, respectively, during the 20 weeks of buserelin treatment. During treatment, E2 concentrations remained below 50 pg/ml in 98 of 116 weekly observations. Uterine fibroids shrank after 8 or 10 weeks of buserelin administration, as assessed by ultrasound or gynecological examination. Compared to their initial volume, mean uterine fibroid volume after 20 weeks of buserelin infusion decreased from 220 +/- 51 to 98 +/- 26 cm3, which was 39.4 +/- 6.9% of the pretreatment volume. We conclude that sc administration of a LHRH agonist beginning in the luteal phase markedly reduced the size of uterine leiomyomata, suppressed, but did not abolish, pituitary and ovarian function, and warrants further evaluation as an option or adjunctive therapy to uterine myomectomy or hysterectomy.