The problem of photochemical oxidant pollution, 98% of which is ozone, is addressed. Ozone itself is not the cause of all adverse effects (e.g., peroxyacetyl nitrites cause eye irritation). The typical sequence in the development of oxidant pollution is an initial increase in nitrous oxide, followed by nitrogen dioxide, followed by ozone. These pollutants can be carried long distances and may have long range effects. Ozone is considered by far the most irritant gas to humans, with effects seen even at extremely low concentrations. Dr. Bates reviewed the initial results of a study of hospitalization in the Niagara Peninsula of Ontario as it related to hourly pollution measurement, noting a relationship between elevated ozone and SO2 levels and respiratory admissions within 24 hr during the summer months. This is an important preliminary finding, as EPA data indicate that nitrogen oxides are increasing while other pollutants are decreasing.