City directories and death certificates were used to perform a case control study of bladder cancer deaths in Hamilton County, Ohio. In Hamilton County, 731 male bladder cancer deaths were listed between 1960 and 1982 and 95,057 male deaths from other causes. Two analyses were performed, one based on city directory data and one based on death certificates. Each case was matched for sex, age, race, date of death, and residence to two comparisons. The results indicated that four companies were associated with an increased risk of bladder cancer. NIOSH investigated six facilities that showed an increased risk (two chemical factories, a printing ink company, a foundry, a machine manufacturer, and a valve manufacturer), and several suspected agents were identified. In particular, one chemical factory had produced benzidine (92875), a known human carcinogen, and this facility was the site of a previous epidemic of bladder cancer. In general, increased risks were found for the textile, chemical, grain mill foundry, petroleum, building service, entertainment, and advertising industries. Based on occupations, increased risks were found for engineer, tailor, carpenter, furnace operator, blending machine operator, chemist, pressing machine operator, house cleaner, and salesman. For truck drivers and furnace operators, more than 20 years of service were associated with a significantly increased risk. The authors conclude that a combination of city directories and death certificates can provide the material for reliable and economically feasible studies.