OBJECTIVE We performed a randomized clinical trial to evaluate the efficacy of intranasal 400 micrograms buserelin three times daily for 6 months versus expectant management in the treatment of infertile women with pelvic endometriosis stage I or II of the revised American Fertility Society classification. METHODS Seventy-one consecutive patients (mean age 32 years) were studied at the First Department of Obstetrics and Gynecology, University of Milan, and the Department of Obstetrics and Gynecology, Ospedali Riuniti, Bergamo, between February 1988 and June 1989. Thirty-five women were randomly allocated to buserelin treatment and 36 to expectant management. The baseline distribution of subjects for age, disease stage, and reproductive history was similar in the two groups. All patients were followed regularly; median follow-up was 17 months in the buserelin group and 18 months in the women given expectant management. If pregnancy did not occur within 12 months of randomization, cycles were monitored by ultrasonography and hormone measurements, and when abnormalities were detected clomiphene citrate and human chorionic gonadotropin were administered. RESULTS A total of 17 pregnancies were observed both in the buserelin-treated patients and in the expectant management group. The 1- and 2-year actuarial overall pregnancy rates were similar in the two groups, 30% and 61% in the former and 37% and 61% in the latter group, respectively. Spontaneous abortion occurred in five of the 17 pregnancies in the women treated with buserelin and in one of the 17 in those managed expectantly; this difference was, however, not statistically significant (chi 1(2) adjusted for disease stage and use of clomiphene citrate and human chorionic gonadotropin treatment = 3.01, p = 0.08). No fetal death or stillbirth was observed. CONCLUSIONS Our findings suggest that treatment with gonadotropin-releasing hormone agonists is unlikely to have a marked influence on the reproductive outcome of infertile women with minimal or mild endometriosis.