The study represents an extension of research begun under a contract (No. 68-01-3144) funded jointly by the U.S. Environmental Protection Agency and the U.S. Department of Transportation entitled, 'Air Pollution and Health in Washington, D.C.: An Analysis of Some Acute Health Effects of Air Pollution in the Washington Metropolitan Area.' In the original study three basic categories of data were analyzed: health information, air quality measurements, and weather factors. Since undertaking that analysis, additional air pollution and weather data became available. This study has attempted to examine the implications on previous conclusions of analyzing this expanded data base. The study period was again 1973-74 and focused on the Washington, DC Metropolitan Area. Statistical models were formulated to test the hypothesis that air pollution can aggravate the health status of a population and can result in increased utilization of certain types of medical care services. The statistical results indicated that air pollution levels had a very limited effect on the health-care utilization of the group practice even after the additional air pollution and meteorological data were examined.