Estuaries are ecosystems of high productivity, crucial in the life history of fishes, invertebrates, birds, including commercially important species, but anthropogenic activities such as urban effluents are often the main factors responsible for water quality degradation. Complex mixtures of contaminants are present in these zones and in this context; there is a growing interest in the influence of endocrine disruptor compounds (EDCs) on biota physiology. The Loire estuary runs through important urban sites (Nantes, Saint-Nazaire, etc.) with shipping and industrial activities. Moreover, the Loire basin (117,000 km²) represents more than 1/5 of the French territory and drains a lot of tributaries. The aim of this research is to evaluate the contamination of the Loire estuary by EDCs. Twelve sites along the Loire estuary (from Saint-Nazaire to Ancenis) were selected because of their typology of contamination (agricultural, urban, and industrial) and of their particular configuration (upstream/downstream of an effluent site close to a wastewater treatment plant). The endocrine activities in sediment were followed using various bio-analytical tools (in vitro tests of hormonal activities on cellular cultures). The presence of PAHs and dioxine-like compounds was estimated using the EROD test. The eel Anguilla anguilla was chosen for her ecological representativeness and economical incidence on fishing activities and was collected on 3 sites along the Loire estuary (upstream, intermediate, and downstream). The in situ effects on fish were evaluated by measuring biological variables at the individual level (size, sex, gonads histology, vitellogenin and aromatase).