Successful development of a commercial, small-mesh trap net fishery for round whitefish ( Prosopium cylindraceum) in Saginaw Bay, Lake Huron, prompted analysis of round whitefish fillets for selected contaminants [dieldrin, dichlorodiphenyl trichloroethane and metabolites (DDT), polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), chlordane, methyl mercury, and total mercury] to determine the fish's suitability for human consumption. Concentrations of all contaminants measured in 1977–1978 were below U. S. Food and Drug Administration action guidelines for fish; PBBs were below detection limits (0.001 mg/kg) for all fillets analyzed. Only PCBs and total DDT residues displayed a strong direct relationship with fish length. Fillets from males consistently exhibited higher mean concentrations of contaminants than did females. No changes in contaminant levels with season were observed.