The electrolytic removal of ethinylestradiol (EE2), the most potent synthetic estrogen, in effluent of a membrane bioreactor (MBR) treating hospital sewage and in drinking water, was studied at dosed concentrations of about 1 mg EE2 L-1. Removal efficiencies of up to 98% were obtained with supplemental efficient eradications of bacteria (up to 3.4 log units). Residual effects were observed when a treated flow was mixed with an untreated flow. An increasing concentration of NaCl resulted in an enhanced EE2 removal. This effect was more pronounced in MBR effluent than in drinking water. To approach more environmentally realistic concentrations, an experiment with initial concentration of 10 mu g EE2 L-1 drinking water was set up, still resulting in an EE2 removal of 85%. (c) 2006 Society of Chemical Industry.