Polychlorinated biphynels and chlorinated pesticides are ubiquitous marine pollutants that are bioaccumulated by marine mammals and are biomagnified through the food chain. Marine mammals, at the top of their food chain, carry very heavy body burdens of these potentially toxic anthropogenic contaminants. In cetaceans and pinnipeds there is some limited evidence that high body burdens of organochlorines may impair reproduction. There is also evidence that high body burdens and increased whole blood concentrations of these compounds can cause problems with immunological response systems in marine mammals which may make them more susceptible to secondary infections. In order to study the possible chronic tonic effects of chlorinated hydrocarbons on the health of marine mammal populations, data on levels of these compounds in tissues of stranded and healthy animals is needed. Neither the AOCS nor the AOAC have an official method for the determination of pcbs or pesticides in marine oils or tissues. The AOAC has first and final actions for packed column gas chromatographic methods for determination of the compounds in fish and non-fatty foods and the EPA has mass spectroscopy methods for the determination of these compounds in soil and sediment. There is also a gel permeation first action method for organochlorine residues in poultry, beed, and swine fats. The AOAC does not have methods for congener specific analysis of polychlorinated biphynels needed for the toxicological assessment of these compounds. The gas chromatography/mass spectroscopy (GC/MS) procedure described in this technical memorandum is an adaption of these methods that accomodates the matrices, congener specific analysis, sample sizes and analyte levels encountered in the analysis of marine mammal tissues.