Evidence is accumulating that elevated levels of serum IgE may play a role in the pathogenesis of chronic airflow obstruction. We examined this question using data on 863 subjects drawn from two cohort studies which we have followed over a period of nine to 11 years. One, the Portland cohort, represents a working population aged 25 to 55 years at baseline. The second, the Screening Center cohort, spans a wider age range (18 to 87 years at baseline) and is biased towards respiratory disease. Spirometric tests and respiratory symptom questionnaires have been administered five times over a nine-year period for the Portland cohort, and over an 11-year period for the Screening Center cohort. IgE was measured one time towards the end of the follow-up. Our data confirm the finding that smokers tend to have higher IgE levels than nonsmokers. For the combined sample, geometric mean levels of IgE were 31.0 IU/ml among smokers and 17.4 IU/ml among nonsmokers. Levels among ex-smokers were intermediate. Among smokers, IgE was not related to either amount smoked or pack-years. Cross-sectionally, FEV1 was inversely related to IgE in the Screening Center cohort, but not in the Portland cohort study. Among smokers, this association was only present for those subjects with symptoms of chronic bronchitis (chronic cough/sputum production). We found no association of IgE with longitudinal rate of decline of FEV1 in either cohort. These findings are consistent with other studies and support the hypothesis that serum IgE is inversely related to function level cross-sectionally, but is not predictive of rate of decline of lung function.