Equilibrium partitioning theory (EPT) and biomagnification for hydrophobic organic chemicals in benthic macroinvertebrates and higher benthic animals were investigated by use of available field data. Animal–sediment concentration ratios were investigated as a function of Kow and of different animal and chemical types and times of sample collection. Under the assumptions in this analysis, EPT was a useful first approximation for data that were sufficiently aggregated; however, there were significant differences in concentration ratios among individual animal-chemical combinations, systematic variations with Kow, and significant seasonal variability. The only evidence for biomagnification was that body burdens for carp were significantly higher than body burdens for all other animal types and significantly higher than expected on the basis of EPT. Body burdens in forage fish were not significantly different from those in benthic macroinvertebrates. © 1990, American Chemical Society. All rights reserved.