We report an interesting case of above-normal serum estradiol concentration of unknown origin. A 30-year-old white woman was seen for infertility problems. Hormonal evaluation revealed the following results. Postovulatory progesterone concentrations and profile (a plot of hormone concentration vs time of cycle) were within the normal range for our laboratory (Table 1). However, the post-ovulatory estradiol concentrations were extremely high, although the curve appeared normal in profile (Table 1).