Human blood serum samples were analyzed using gas liquid chromatography for the presence of polychlorinated biphenyls (1336363) (PCBs) using methanol as a solvent. Extracts were centrifuged, concentrated by evaporation and saponified, and columns were eluted with 50 milliliters of hexane. Quality control was maintained during each sample run by establishing and documenting chromatogram resolution through analysis of a chlorinated hydrocarbon pesticide mixture, blind duplicate samples, reagent blank samples, a chlorinated hydrocarbon pesticide mixture, and two serum pool samples. Each chromatogram was quantitated as Aroclor- 1242 (53469219) and Aroclor-1254 (11097691). Each analytical run contained samples of PCB pool A and 220 and 441 nanograms per milliliter (ng/ml) of Aroclor-1242 and Aroclor-1254, respectively; while pool B contained 405 and 370ng/ml of Aroclor-1242 and Aroclor- 1254, respectively. Confirmation of PCB was accomplished by perchlorination to decachlorobiphenyls using antimony-pentachloride as the derivatizing reagent. Samples from two sites had concentrations of Aroclor-1242 in the 10 to 50ng/ml range; while Aroclor-1254 concentrations were divided between the less than 10ng/ml and 10 to 50ng/ml ranges. Samples from a third site had concentrations of Aroclor-1242 greater than 100ng/ml. Over 80 percent of Aroclor-1254 concentrations were in the 10 to 50ng/ml range. Some samples had Aroclor concentrations greater than 1,000ng/ml. The authors suggest that because of assumptions made in the quantitation of PCB concentrations, the observed of PCBs as Aroclor-1242 and 1254 are probably higher than the concentrations actually present.