Concentrations of Cd, Cu, Fe, Pb and Zn were measured in scales of the seagrass Posidonia oceanica from different areas of the French NW Mediterranean: the Cbte d'Azur and Corsica.Scales are basal parts of the seagrass which remain fixed on the rhizomes when leaves of P. oceanica die. Scales do not decay and the cyclic variation of their thickness permits retroactive dating (lepidochronology). Heavy metal concentrations were determined in the scales of P. oceanlca dated by lepidochronology. Scales from P. oceanica collected from the CBte d'Azur (analysis of lepidochronological years from 1982 to 1992) generally showed concentrations of Cu. Fe. Pb and Zn to be greater lharr those measured in samples from Corsica (analysis of lepidochronological years from 1972 to 1992).In contrast, Cd concentrations recorded in scales from Corsica were higher than in those from Cbte d'Azur. The reasons for these high Cd values are unknown. There was a general tendency for metal concentrations in P oceanlca scales collected on the C6te d'Azur to decrease with time. In Villefranchesur-Mer, where there are many pleasure boats, large concentrations of Cu were found in P. oceanica scales. These concentrations had increased in recent years.