Although the role that LH plays in folliculogenesis is still controversial, recent evidence points toward facilitatory actions of LH activity in ovulation induction. Thus, we compared the response to either highly purified FSH (75 IU FSH/ampoule; group A, 25 subjects) or human menopausal gonadotropin (75 IU FSH and 75 IU LH/ampoule; group B, 25 subjects) in normoovulatory GnRH agonist-suppressed women, candidates for intrauterine insemination. A fixed regimen of 2 daily ampoules of highly purified FSH or human menopausal gonadotropin was administered in the initial 14 days of treatment; menotropin dose adjustments were allowed thereafter. Treatment was monitored with daily blood samples for the measurement of LH, FSH, 17beta-estradiol (E(2)), progesterone, testosterone, hCG, inhibin A, and inhibin B, and transvaginal pelvic ultrasound was performed at 2-day intervals. Although preovulatory E(2) levels were similar, both the duration of treatment (16.1 +/- 0.8 vs. 12.6 +/- 0.5 days; P< 0.005) and the per cycle menotropin dose (33.6 +/- 2.4 vs. 23.6 +/- 1.1 ampoules; P < 0.005) were lower in group B. In the initial 14 treatment days the area under the curve of FSH, progesterone, testosterone, inhibin A, and inhibin B did not differ between the 2 groups, whereas LH, hCG, and E(2) areas under the curve were higher in group B. The occurrence of small follicles (<10 mm) and the inhibin B/A ratio in the late follicular phase were significantly reduced in group B. A nonsignificant trend toward a higher multiple gestation rate was present in group A (60% vs. 17%). We conclude that ovulation induction with LH activity-containing menotropins is associated with 1) shorter treatment duration, 2) lower menotropin consumption, and 3) reduced development of small ovarian follicles. These features can be exploited to develop regimens that optimize treatment outcome, lower costs, and reduce occurrence of complications such as multiple gestation and ovarian hyperstimulation.