The role of immunoglobulin E (IgE) in the development and course of impaired ventilatory function and chronic obstructive pulmonary disease (COPD) required further study. This role has been examined in the longitudinal Tucson Epidemiological Study of Airways Obstructive Disease, which started in 1972. The association between IgE and longitudinal changes in pulmonary function measures was examined in subjects in the community population sample in Tucson who had an initial age of 35 or more. There were a total of 1,533 such subjects with lung function tests over the 20 yr period who also had IgE determinations. A significant inverse association was found between total serum IgE and FEV1/FVC that was independent of smoking and asthma status. The finding was statistically separate from the relation with age in all but elderly current smokers (age > 55). The magnitude of this effect in nonasthmatic subjects was relatively small. For asthmatic subjects, however, the inverse association was larger in both current and never smokers. Subjects excluded from the current analysis either did not have an IgE measurement and/or had no pulmonary function values after 35 yr of age. These findings suggest that higher IgE levels may indicate the presence of a disease process that may involve inflammation and/or other mechanisms related to IgE production, which impair lung function over time. However, in this study we were not able to account for possible parental or inheritance contributions to increases in total IgE, which have been shown to be important.