Several studies have reported the associations between airborne particles and/or ozone and respiratory diseases. This study examined whether such an association could be seen in Seoul, one of the greatest city in Korea. We compiled daily records of hospital visits in Seoul from November 1, 1995 to October 31, 1996. The daily averages of ozone and particle matter whose diameter is 10 micrometer or less(PM10) from all monitoring stations were computed. Daily respiratory hospital visits were regressed on temperature, humidity, day of weak indicators, seasonal variation indicators, and air pollution. Each pollutant was first examined individually and then two pollutant models were fitted. RESULTS : Both PM10 and Ozone were associated with increased risk of respiratory hospital visits. The relative risk of respiratory hospital visits for 50 microgram/m3 increase in PM10(lagged 2 days) was 1.11(95% confidence interval: 1.05-1.18). The PM10 associations was insensitive to alternative methods of control for weather, including exclusion of extreme temperature days and control for temperature on another day. The ozone results were more sensitive to the approach for weather control. The relative risk of respiratory hospital visits for 0.01 ppm increase in O3 was 1.08(95% confidence interval 1.00-1.17). The magnitude of the PM10 effect in Seoul, where SO2 was essential present, was similar to that reported in the Europe and United states. In conclusion, The consistency of investigations of the health effects of air pollution suggest that attention should be paid to the control of air pollution.