[Changes in the density gradient distribution of erythrocytes during the menstrual cycle]

Modifications in erythrocyte density distribution were evaluated, by means of centrifugation on Ficoll-Triosil discontinuous density gradient, in five healthy young women during menstrual cycle. Oestradiol and progesterone plasma levels were tested, showing normal and typically ovulatory-like variations during the cycle. Youngest cell populations showed always quantitative increases from the follicular to the ovulatory phase of the cycle, reverting to basal values in the luteal phase. Possible hormonal or haemorrhagic causes are discussed.