Polychlorinated biphenyls (PCBs) are a highly lipophilic group of global pollutants, consisting of 209 congeners. PCBs were discovered before the turn of the century and their usefulness for industry, because of their physical properties, was recognized early. The distribution of PCBs in the environment was not noticed until Jensen and his colleagues found PCBs in wildlife samples. Since then, investigations in many parts of the world have revealed the widespread distribution of PCBs in environmental samples and PCVs are persistent and accumulate in food webs. Thus, determination of toxicities of commercial PCB mixtures and PCB congeners are required. Toxicity tests using luminous bacteria have shown high correlation to traditional bioassays. This study compared the EC50 values of the commercial mixtures, PCB3 and PCB5, with those of Aroclor 1242 and Aroclor 1254. 12 refs., 2 tabs.