Abstract In 1972, investigators from the National Institute for Occupational Safety and Health (NIOSH) were informed of a report of a cluster of liver cancers at a plant in Louisville, Kentucky, that produced polyvinyl chloride (PVC) plastic products. This plant opened in 1942 and produced both the monomer gas (VC gas) and the polymerized plastic (PVC) through 1966. In 1966, the plant stopped production of VC gas, but continued to buy the gas and to produce PVC products. About three-quarters of the men who had worked at the plant had been exposed to both VC gas and PVC dust.