['Human epididymal secretory protein E4 (HE4) is a new promising tumor marker developed for the diagnostics and follow up of ovarian cancer. It has yet to become widely accepted in clinical practice, and its biological properties have not been inclusively studied. The aim of this study was to investigate whether serum HE4 concentration varies within the normal menstrual cycle and whether common gynecological hormonal treatments have an effect on HE4 values.', 'Our study population consisted of 180 women, including 126 endometriosis patients and 54 healthy women. We measured their serum HE4 and CA125 concentrations and evaluated the effect of the menstrual cycle and the possible hormonal medication on these marker concentrations.', 'We found no significant variation in serum HE4 concentrations in samples taken at different phases of the menstrual cycle. The median HE4 concentrations in proliferative, secretory and menstrual phase were 41.5, 45.1 and 35.3 pM in healthy women, and 43.4, 44.3 and 43.0 pM in endometriosis patients, respectively. The use of combined estrogen and progestin contraceptives did not affect serum HE4 levels significantly.'] Is serum HE4 concentration dependent on menstrual cycle or hormonal treatment among endometriosis patients and healthy premenopausal women?