Drs. Matanoski and Tao at Johns Hopkins University examined the relationship between styrene exposure and heart disease in workers in styrene-butadiene polymer manufacturing plants between 1943 and 1982. Workers who had died from ischemic heart disease were compared to a subgroup of all men employed in two styrene-butadiene polymer manufacturing plants during that time. Individual exposure histories were determined from job records, or constructed using a statistical method to estimate exposure when records were missing. This method was based on the assumption that exposure concentrations in all jobs in a plant are normally distributed and that processing methods throughout the rubber industry did not change appreciably during the time under consideration.