This study of the hospitalization costs of exposure to air pollution in Allegheny County, Pennsylvania was conducted to determine whether persons exposed to air pollution incurred higher hospital utilization rates and additional costs for treatment. A hospitalization data-base comprising 37,818 total admissions for respiratory, suspect circulatory diseases, and comparison circulatory diseases was tested in a cross-section type analysis for relationships between rates of hospitalization, length of stay, and levels of air quality in the neighborhoods of patients' residence. Air quality was identified using data from 49 monitoring stations. Corrections were made for race, age, sex, smoking habits, median income, and occupation. The results show that hospitalization rates, length of stay, and costs of respiratory and suspect circulatory system diseases were significantly greater among populations residing in the more polluted zones of the County. At average costs for hospitalization in this area in 1972, the total increased cost for the 1.6 million persons in the County was estimated at $9.8 million ($9.1 million for increased hospitalization rates and $0.7 million for increased length of stay). The total health costs resulting from air pollution exposure in this area would be much greater when non-hospitalization costs are also included.