In Dec. 1973, 8 ruddy ducks [Oxyura jamaicensis] killed in an oil spill on the Delaware River [USA] were collected to be analyzed for residues of environmental pollutants. Whole carcasses were analyzed for organochlorine pesticides and livers were examined for Pb, Cd and Hg. Residues of polychlorinated biphenyls and DDT and/or its metabolites were present in all carcasses. Dieldrin and hexachlorobenzene were present in 7 of the 8 samples. All livers contained detectable levels of Pb, Cd and Hg.