Trace-metal concentrations (Cd, Cu, Fe, Mn and Zn) were investigated in two species of abundant filter-feeding molluscs from Mauritania, the wedge shell Donax trunculus L. and the clam Venus verrucosa L. D. trunculus were collected on the beach of Nouakchott at low tide and V. verrucosa were sampled at the "Banc d'Arguin" at depths varying from 10 to 20 m, in mid-February 1987. D. trunculus contains significantly higher Fe and Zn concentrations than the clam. Total trace-metal content per individual (I1) in D. trunculus could be related to body weight (W) as the power function Y--a W b. The subsequent regression coefficient b was < 1 for Cu, Fe, Mn and Zn and > 1 for Cd. Metal concentrations in both species decreased in the order: Fe>Zn>Mn>Cu>Cd. Comparison of trace-metal concentrations in the small D. trunculus and the large V. verrucosa revealed lower contents in V. verrucosa, except for Cd. The trace-metal distribution in the various organs of V. verrucosa indicates that gills seem to concentrate metals, except Cu, to a greater degree than the other organs (visceral mass and "remainder"). The relatively elevated content of Fe in D. trunculus and of Cd, Fe and Zn in the gills of V. verrucosa seem to be of natural origin. In view of the scarcity of Mytilus sp. along the Mauritania coast, the molluscs D. trunculus and V. verrueosa are proposed as useful bioindicators of trace-metal concentrations.