Daily levels of sex hormones in 15 subfertile women formulate a menstrual cycle profile predominant with progesterone secretion.

1. Throughout the entire menstrual cycle length in subfertile women, P4 secretion predominates quantitatively over secretions of the remaining sex hormones when menstrual cycle phases are hidden. 2. The rise of E2 secretion is in parallel with the P4 rise, but with 4 times lower amplitude of E2. 3. T secretion declines and is inversely related to both P4 and E2 secretions. 4. Changes in E2 bioavailability are related to menstrual cycle length.