We compared ovulatory changes in fertile and preceding infertile cycles in 21 patients with unexplained infertility conceiving after clomiphene citrate treatment. No significant differences were observed in follicular growth, cervical score and follicle stimulating hormone (FSH) levels. Progesterone was higher (P less than 0.05) in the 2 days preceding ovulation in fertile cycles, luteinizing hormone (LH) higher (P less than 0.05) the day before, and 17-beta-estradiol lower (P less than 0.05) 4 days before. Stimulating progesterone secretion by systematic LH administration before ovulation could improve secretory endometrial transformation and thus reproductive prognosis.