An analytical procedure was developed that enables routine analysis of four estrogenic hormones in concentrations below 1 ng/l in surface water and waste water. The recovery was 88-98% with a limit of detection of 0.1-2.4 ng/l depending on the compound and the matrix measured. This method was used to determine the occurrence of 17 beta-estradiol, 17 alpha-estradiol, estrone and 17 alpha-ethinylestradiol in the aquatic environment in The Netherlands. The data show that estrogenic hormones can be detected at low concentrations (up to 6 ng/l) at some locations in surface water. In selected effluents of waste water treatment plants estrone and 17 beta-estradiol were detected in concentrations in the ng/l range. Concentrations of 17 alpha-estradiol and the contraceptive 17 alpha-ethinylestradiol were in most of these samples below the limit of detection. Hormone glucuronides were not detected in most surface water and effluents.