Sediment passing through the intestinal tracts of aquatic organisms can cause marked overestimation of metal levels (i.e. true biologically incorporated metals) even in specimens collected from unpolluted waters. In the present study, 42 male caplin Mallotus villosus, collected from an apparently unpolluted site in Newfoundland were analyzed for 22 elements using ICPMS. All but three of the caplin were found to have sediment in their intestinal tracts. A high degree of correlation was observed between the amount of sediment in the specimen and the concentrations of a number of metals (especially aluminum, manganese, iron). The individual caplin with the most sediment had an aluminum concentration of 696 μ/g, a manganese concentration of 24·8 μ/g and an iron concentration of 784 μ/g. By comparison, the sediment-free caplin showed much lower levels of 3·84 μ/g for aluminum, 2·09 μ/g for manganese and 41·2 μ/g for iron. Thus, metals bound to sediment in the intestinal tracts of marine organisms can clearly interfere with the determination of the true level of metals incorporated into the organism's tissue. The sediment-bound metal may not be available to either the organism or its predators but may be released by acid dissolution of the specimen during analysis. In specimens taken from areas with metal-enriched sediments, overestimation of true tissue concentrations may result.