The effect of oxidant inhalation on allergic illness is of interest because allergic patients often report increased respiratory symptoms during episodes of poor air quality, and epidemiologic studies demonstrate an association between increased levels of the air pollutant ozone and exacerbations of asthma. The purpose of this study was to characterize the upper respiratory response to ozone inhalation in asymptomatic, allergic subjects and to determine whether ozone pre-exposure increased the acute response to nasal challenge with antigen in these subjects. A group of 12 asymptomatic subjects with a history of allergic rhinitis were exposed in a randomized, cross-over design, at rest, on each of 2 days, separated by 2 wk, to 4 h of clean air or 0.5 ppm ozone in an environmental chamber. Following the exposure period, subjects underwent nasal challenge with four doses of antigen (1 to 1,000 PNU ragweed or grass). Symptoms were rated and nasal lavage performed after each dose. Measurement of histamine and albumin concentration and TAME-esterase activity and determination of cell counts and differentials were performed. Exposure to ozone caused significant increases in upper and lower respiratory symptoms, a mixed inflammatory cell influx with a sevenfold increase in naval lavage neutrophils, a 20-fold increase in eosinophils, and a tenfold increase in mononuclear cells, as well as an apparent sloughing of epithelial cells. There was a significant increase in nasal lavage albumin concentration on the ozone exposure day and a small increase in nasal lavage histamine concentration on both the ozone and clean air exposure days. TAME-esterase activity showed no significant increase overall, but increased at least twofold in 5 of 12 subjects. (ABSTRACT TRUNCATED AT 250 WORDS)