The idea that terrestrial isopods regulate copper intake through the state of their copper stores by selection of an optimal copper diet has never been experimentally assessed. We investigated discrimination between untreated and Cu-enriched diets in the isopod Porcellio scaber in relation to their copper stores. Animals were pre-exposed to untreated or Cu-enriched poplar leaves. After 14 and 28 days of pre-exposure, two-way food choice experiments were performed for 14 days. Food consumption rates and the amount of copper accumulated due to the copper content of the food and the duration of pre-exposure were compared. Food selection and rejection as ways by which P. scaber may reduce or avoid the toxic effects of copper were evaluated. P. scaber offered both Cu-enriched food and untreated food preferred the latter, irrespective of the amount of assimilated copper. Copper body burdens increased with copper concentration in the food. In animals offered both Cu-enriched and untreated food, copper body burden also increased, but to a lower extent than in animals fed only a Cu-enriched diet. Therefore, food selection is a way of regulating copper intake, but only to a limited extent. The mortality of experimental animals increased significantly after longer exposure to highly Cu-enriched food. We conclude that in P. scaber, the possibility of selecting food of different copper content may mitigate but cannot prevent the toxic effects of copper in copper-polluted environments. © 2003 Elsevier B.V. All rights reserved.