Premenstrual endometrial biopsies were performed in 324 infertile women. Their hormonal status was established in the early follicular phase of the same cycle (FSH, LH, oestradiol-17 beta, testosterone, DHEAS, TSH and prolactin, the latter two both basally and following TRH stimulation). In the luteal phase, oestradiol-17 beta and progesterone concentrations were determined three times between the fifth and tenth hyperthermic days, as was prolactin, both basally and following metoclopramide stimulation. All pregnancies occurring before January 1986 were recorded. Seventy-five per cent of the biopsies were evaluated on the expected ovulation date from the basal temperature charts, 77% according to the next onset of menstruation. Twenty-six per cent of the biopsies were out of phase, and 7% displayed abortive secretion. A significant correlation existed between endometrial profiles and the characteristics of the cycle, stimulated TSH and prolactin levels, and with testosterone and FSH concentrations. No correlation of the endometrial status with midluteal oestradiol or progesterone concentrations was found. While various hormones of both the follicular and luteal phases correlated significantly with the pregnancy rate, the same was not demonstrated for the state of endometrial biopsy. Therefore, following exclusion of organic explanations of infertility in women with biphasic cycles, the determination of progesterone and oestradiol-17 beta in the luteal phase was considered. In women with reduced concentrations of these hormones, androgens, gonadotrophins, prolactin and TSH should be determined. Endometrial biopsy is valuable only if pregnancy fails to occur, despite therapeutically normalized hormone concentrations.