An increase in prevalence of wheezing illness in the UK has coincided with a reduction in the consumption of natural antioxidants, which may modulate the lung's response to oxidant stress, limiting the expression of airway inflammation and respiratory symptoms. The hypothesis that intakes and plasma levels of natural antioxidants would be determinants of adult-onset wheezing illness was tested. A nested case-control study was conducted in 94 cases with adult-onset wheeze and 203 controls aged 39-45 yrs identified in a 30-yr follow-up survey. Antioxidant intake was measured by a food frequency questionnaire, and plasma and red cell measurements of antioxidant status were obtained. Outcome measures were onset of wheeze since age 15 yrs (ever wheeze) and wheeze occurring in the past 12 months (current wheeze). After adjusting for the effects of smoking, socioeconomic status, atopy, family history of atopic disease and total energy intake, intakes of vitamin E (odds ratio (OR) = 4.02 for low compared to high tertile of intake) and plasma levels of ascorbate (OR = 0.98 per unit) and alpha-tocopherol:triglyceride ratio (OR = 0.34 per log(e) unit) were inversely related to adult-onset wheeze. In analyses stratified by social class and smoking, intakes of vitamin C and E and plasma levels of ascorbate and alpha-tocopherol:triglyceride ratio were inversely related to current wheeze in the manual social class and among current smokers. No independent associations of vitamin A, beta-carotene or total plasma antioxidant capacity were found. The results support the hypothesis that deficiencies of vitamins C and E are associated with wheezing symptoms. Smokers in the manual social class are particularly susceptible to these effects.