Imposex (the development of male sex organs on the female) has been studied in the European sting winkle, Ocenebra erinacea. In common with studies of other gonochoristic stenoglossan gastropods, the evidence gained from surveys of the south-west regions of England and Brittany (France) indicates that the phenomenon is a response to tributyltin (TBT) pollution. Close to sources of TBT, O. erinacea females exhibit structural abnormalities of the oviduct as a result of advanced imposex, including absence of a genital papilla and a normal vulva, a deformed bursa copulatrix and the presence of a longitudinal split. Copulation and capsule formation would appear to be inhibited in the worst-affected females. Such curtailment of breeding activity would result in population decline: direct evidence of the extinction of O. erinacea close to harbours, as is known for N. lapillus, is generally wanting for British shores, but the decline of the species in the Bay of Arcachon in France is attributable to TBT pollution.