Catecholestrogens, 2-methoxyestrogens and "classical" estrogens (estrone, estradiol, estriol) were measured simultaneously in urine samples of healthy women during the menstrual cycle. All estrogen values reach a preovulatory maximum at the time of the LH peak and show a marked increase during the luteal phase as compared to the follicular phase. Catecholestrogens and estrone seem to behave similarly supporting the assumption that catecholestrogens are predominantly metabolites of estrone. Daily measurements of urinary estrogens show large interindividual variations of 2- and 4-hydroxyestrogens as well as very differing 2-hydroxy-/2-methoxyestrogen ratios. The results obtained support the assumption, that catecholestrogens and their methylethers are excretory products with no additional regulatory functions.