Estrogenic disrupting potency was studied in rivers and wastewaters in the Orge catchment near Paris area, using analytical and biological approaches simultaneously. The MELN test was applied to surface water samples, urban storm runoff and WWTP effluent in parallel to analytical determinations of natural estrogens and synthetic estrogen (ethinylestradiol) using liquid chromatography and tandem mass spectrometry. Estrone was quantified in all samples, from 0.1 to 15.7 ng·L-1. b-Estradiol was also quantified in all samples, but at a lower level: from 0.1 to 2.3 ng·L-1. a-Estradiol was never detected. Ethinylestradiol was only quantified in WWTP effluent (0.2 ng·L-1); Estriol was measured in WWTP effluent (12.1 ng·L-1) and downstream effluent (4.9 ng·L-1). The biological responses using the MELN test closely followed the chemical ones. Analytical quantification of estrogens appears to be a simple way to trace estrogenic disruption in surface waters of urban areas as these hormones are the main responsible of effects.