Blood samples were obtained during early follicular, periovulatory, and luteal phases in four women with out-of-phase endometrial biopsy specimens and four normal controls. In the study cycle, follicular development was evaluated and a late luteal phase endometrial biopsy was performed in each subject. Area under the luteal phase progesterone curve positively correlated with degree of maturity of the endometrial biopsy. Peak serum estradiol, maximum follicular diameter, and both immunoactivity and bioactivity of the preovulatory luteinizing hormone and follicle-stimulating hormone surges were similar in the luteal phase defect cycles as compared with normal cycles. Likewise luteinizing hormone bioactivity in the luteal phase of the luteal phase defect cycles was similar to that of normals. These data show that the immunoactivity and bioactivity of periovulatory and luteal phase gonadotropins may be normal in luteal phase defect cycles.