A morbidity and mortality study of workers at an alcohol manufacturing plant which included several weak acid isopropyl alcohol units and a strong acid ethanol unit is described. An excess mortality of upper respiratory cancer was found and associated with work on the strong acid ethanol unit. The strong acid ethanol process used resulted in high concentrations of diethyl sulfate, which has been shown to be carcinogenic in animals, and the unit, which closed in 1975, had significant opportunities for worker exposure to diethyl sulfate. These facts, plus previous reports of excess upper respiratory cancer on strong acid isopropyl alcohol units with similarly high concentrations of the animal carcinogen diisopropyl sulfate, lead to the tentative conclusion that diethyl sulfate was primarily responsible for the ethanol unit cancer cases. In the modern weak acid isopropyl alcohol plants, where only trace amounts of diisopropyl sulfate are present and exposures are much lower, the problems found on the old strong acid units do not exist.