The report describes ozone and PAN levels at urban sites in the U.S., and of ozone at selected nonurban sites. Sample diurnal curves for ozone at suburban and nonurban sites are presented. Highest concentrations of both oxidants occur in California, where the second-highest 1-hr concentration of ozone in 1983 was 0.37 ppm, and the highest PAN concentration reported in this decade was 0.047 ppm, in 1980. At selected nonurban sites, maximum 1-hr ozone levels for 1978-1981 were about half the second-highest 1-hr ozone levels at urban sites in those years. Examples presented of temporal patterns of ozone show distinct seasonality at suburban versus nonurban sites, and point out potential implications for exposures to ozone of populations, vegetation, and other receptors. Data on co-occurrences of ozone with nitrogen dioxide or sulfur dioxide indicate relatively few such events at levels of potential concern for vegetation and public health.