A review of the data and a summary of findings regarding the potential human health hazards of polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p- dioxins (PCDDs), and related compounds resulting from electrical equipment fires or failures were presented. Physical and chemical properties of PCBs, use of PCBs in electrical equipment, potential for exposure to PCBs and related compounds following fire or failure of electrical equipment, and exposure limits were presented as background data. Toxic responses noted in PCB, PCDF, or PCDD treated animals are analogous, however, individual compound potencies vary with regard to the degree and position of chlorination. A soot sample collected after a transformer fire in New York in 1981 yielded 5000 micrograms/gram (microg/g) PCBs, 48microg/g 2,3,7,8-tetrachlorodibenzofuran (51207319), and 1.2microg/g 2,3,7,8-tetrachlorodibenzo-p-dioxin (1746016). The median lethal dose (LD50) of the soot in aqueous methyl-cellulose, when administered in a single oral dose in guinea-pigs, was 410mg/kg; the LD50 of a benzene extract of the soot was 327mg/kg. Reported health effects in humans upon exposure to PCBs include chloracne, hyperpigmentation, gastrointestinal disturbances, elevated serum enzyme and triglyceride levels, and numbness of the extremities. As prudent public health policy, NIOSH recommends that occupational exposure to PCBs, PCDFs, and PCDDs resulting from electrical equipment fires or failures be controlled to the lowest feasible limit. Keeping occupational exposures as low as possible involves recognition of potential hazard, assessment of exposure, personal protective clothing, respiratory protection, decontamination and worker protection programs, post decontamination testing, and medical surveillance.