Samples of sediments and eel taken from six Amsterdam freshwater sites were analyzed for polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs). Biota-sediment accumulation factors (BSAFs) were determined from levels in sediments [ng/g organic matter (OM)] and eel muscle tissues [ng/g lipid weight (LW)]. Bioaccumulation patterns were both site- and analyte-specific. Bioaccumulation of these persistent organic trace pollutants in eel is discussed, considering partitioning, uptake from contaminated water (bioconcentration) and food (biomagnification), clearance, and bioavailability. Trends in bioaccumulation profiles indicated the following. Levels of PCBs, DDTs, HCB, PCDFs and PCDDs in eel tissues appeared to be exposure related since they increased with increasing levels of pollution in sediments. High BSAF values indicated that biomagnification contributed significantly to the total bioaccumulation process for PCBs, DDTs and HCB. Higher BSAF values for the higher chlorinated PCBs might be due to a more efficient biomagnification of these congeners and to a selective metabolism of the lower chlorinated congeners. Bioaccumulation of HCHs, drins and heptachlor compounds was low in eel. Bioaccumulation of PCDF and PCDD congeners was extremely low in eel. BSAF values of these congeners decreased with increasing chlorine substitution. A large variation in BSAF values for most of the hydrophobic chemicals was observed between different sites. This suggests that bioaccumulation not only depends upon type of organism and analyte, but that site-specific factors should also be taken into account. This might be due to differences in bioavailability (including desorption kinetics) of the compounds or to differences in the diet of the fish when biomagnification is involved. Estimated PCB toxic equivalent values (TEQs) were higher than calculated PCDF/ D TEQs at the reference site. The opposite was found at the most polluted site.