This report is the latest in HEI's program of studies to assess the health impacts of air quality actions. Research Report 148 describes a study to evaluate the effect of a short-term, temporary intervention to reduce traffic congestion during the 1996 Summer Olympic Games in Atlanta, Georgia. A previous study had shown a decrease in acute care visits for pediatric asthma and a concomitant decrease in concentrations of ozone, particulate matter, and carbon monoxide. Because it was not clear to what extent normal seasonal patterns in pollutant concentrations or health outcomes may have influenced the results, Dr. Peel and colleagues evaluated wider time windows surrounding the Olympic Games period and extended the analyses to earlier and later years and to broader geographic areas. They also evaluated additional respiratory and cardiovascular health outcomes in adults.