Although the polychlorinated biphenyls (PCBs) have been used in a wide variety of industrial applications in the U. S. from 1930 until 1970, when their distribution was voluntarily restricted to closed systems, there is scant information on human exposure to adverse human health effects in the U. S. In the U. S., minimal human exposure of the population to PCBs is-limited to food, air, and water, while significant human exposure appears to be limited to sports fishermen consuming fresh water fish from contaminated streams and lakes; and to occupational exposure in industrial workers.