Serum progesterone concentration and urinary pregnanediol excretion were measured simultaneously in 54 patients. The values have a logarithmic distribution. Mean values and normal range were: for serum progesterone in proliferative phase, 0.44 ng. per milliliter (0.15 to 1.30); in secretory phase, 5.6 ng. per milliliter (1.79 to 17.65); for urinary pregnanediol in proliferative phase, 0.42 mg. per 24 hr. (0.15 to 1.20), in secretory phase, 3.48 mg. per 24 hr. (1.22 to 10.13). The correlation coefficient between serum progesterone and urinary pregnanediol is 0.82, and there is almost no discrepancy between the levels of these two hormones. It is suggested that a single hormonal determination after day 20 of the cycle could be sufficient for the detection of a functioning corpus luteum, and preference is given to the progesterone measurement. In anovulation and secondary amenorrhea, lack of cyclic variation occurred and progesterone remained within proliferative phase range. In prolonged cycles, a premenstrual rise of progesterone was observed in some cases, suggesting late ovulation. In hirsutism without polycystic ovaries, hormonal evidence of ovulation was sometimes present. A luteal phase defect was suggested by persistent progesterone concentrations in the lower range of the luteal phase, often associated with abnormal basal body temperature and an atypical endometrial biopsy. Clomiphene citrate induced ovulation in some patients but in half of them a lower extent and shorter duration of progesterone rise were observed as compared to normal cycles, suggesting a probable luteal deficiency. © 1974. ; SCOPUS: ar.j ; info:eu-repo/semantics/published