A methodology is presented for the routine determination of specific polychlorinated biphenyl (PCB) congeners in serum and milk samples. The procedures include standardized extraction, cleanup and quantitation by high-resolution gas chromatography (GC) and comprehensive quality assurance program to minimize systematic and erratic errors. The analyses of 68 PCB congeners and three pesticides, p,p1-dichloro diphenyl dichloro ethylene (DDE), hexachlorobenzene (HCB), and Mirex, at part-per-billion levels include the addition of surrogate congener standards (IUPAC isomers #46 and #142), extraction with hexane after protein precipitation, cleanup with Florisil, and analysis by GC with capillary column and electron capture detection. Quantitation is based on calibration standards and response factors using isomers #30 and #204 as internal standards. The quality control activities consist of analyses of samples in batches of 6 to 10 simultaneously with quality control (QC) samples. The quality assurance program checks that the procedures are under control by the use of control charts and set the criteria for data acceptability. The detection limits for the congeners and pesticides associated with the analyses of 500 serum samples and of 100 milk samples are reported. In addition, typical profiles of congener distribution in both matrices are illustrated.