Polychlorinated biphenyls are widely used industrial compounds marketed in the United States under the trade name Aroclor. They have appeared in fish and wildlife tissues in this country and Europe. They are known to be toxic, but more importantly, their presence in samples along with the commonly occurring organochlorine pesticides complicates the analysis to a serious degree, making identification of pesticide residues by GLC without preliminary separation extremely unreliable. Residues of both polychlorinated biphenyls and organochloride pesticides were present in eagle carcasses. Many of the polychlorinated biphenyl components had retention times identical with those of certain organochlorine pesticide residues. Identification was accomplished by preliminary separations on thin layer plates followed by combined GLC- mass spectromtry.