Dietary factors may influence inflammatory and antioxidant activity, and hence the development of chronic respiratory symptoms. To examine this hypothesis, the authors analyzed data from the Second National Health and Nutrition Examination Survey (NHANES II). NHANES II was conducted on a sample representative of the civilian, noninstitutionalized US population, which included 9,074 white and black adults aged 30 years or older. Dietary factors were derived from serum levels and from a 24-hour dietary recall questionnaire. The authors examined the relations of these dietary factors to the presence of currently active respiratory symptoms. The relation of serum vitamin C, dietary vitamin C intake, dietary fish intake, the ratio of dietary sodium to dietary potassium, and the ratio of serum zinc to serum copper to the respiratory symptoms of bronchitis and wheezing was assessed. Initially, nutrient-specific logistic regression analysis was performed, controlling for age, race, sex, calories, and pack-years of cigarette smoking. When multiple nutrients and total caloric intake were considered for each respiratory symptom outcome, bronchitis was negatively associated with serum vitamin C and with the serum zinc:copper ratio and was positively associated with the sodium:potassium ratio. Wheezing was negatively associated with serum vitamin C, niacin, and the serum zinc:copper ratio. Interactions between nutrients and smoking status were not significant. These data suggest that several dietary constituents may influence the occurrence of respiratory symptoms in adults, independently of cigarette smoking.