Due to the suspected carcinogenic nature of polychlorinated biphenyls (PCBs), a high degree of interest in the analysis and identification of these compounds in transformer oil has developed. The paper reports the identification of Aroclors 1242, 1254, and 1260 in transformer oil samples brought to the laboratory for analysis. One sample contained approximately 450,000 ppm PCB as Aroclor 1260, and required a one to 10 million dilution in order to be analyzed by gas chromatography with electron capture detection. (JMT)