Background. Sorne reports showed that the presence of endocrine disrupting chemicals (EDCs) may be linked to the incidence of intersex in the clam Scrobicularia. plana. Objective. We aimed at assessing the prevalence of intersex in estuaries of NW France and the possible correlation with EDCs. Method. ln thirteen estuaries contaminated at different levels (data from ROCCH, Réseau d'Observation de la Contamination Chimique du milieu marin at http://wwz.ifremer.fr/envliU), intersex and parameters associated with reproduction (sex-ratio, gonadosomatic index) were examined. Clams were collected at the beginning of gametogenesis and at the peak of sexual maturity. lntersex was determined on thin cuts of gonad tissues embedded in paraffin or on gonad smears. The presence of EDCs in sediments collected in parallel with clams was assessed by using an approach combining quantitative chemical analyses of the main classes of EDCs and a battery of in vitro bioassays. Results. Histological observation at the peak of sexual maturity revealed the presence of intersex in sevensites at different levels of intensity from 7 to 57% of males impacted. ln vitro bioassays showed estrogenic activities in all the 13 sites with the highest level in the site where the highest impact of intersex was observed. Androgenic activities were observed only in 3 sites whereas anti-androgenic activities were found in 11 sites. Ali the sites showed dioxin-like activities with different intensity. The observation of thin cuts ofgonad tissues at the beginning of gametogenesis and the chemical analysis of sediments are ongoing to strenghten these findings.