Two hundred seventy-four infertile patients and 43 women with two or more previous first-trimester abortions underwent a luteal function evaluation by basal body temperature, plasma progesterone, estradiol and prolactin determination, and endometrial biopsy (repeated in a later cycle when the first was defective). An endometrial luteal phase deficiency was detected in 37 (13.5%) of the infertility cases and in 14 (32.5%) of the patients with recurrent miscarriage. However, the endometrial defect was associated with normal hormonal levels in the great majority of patients (86.3%).