Individuals with chronic lung disease and their families were selected from the Tecumsch community along with similarly selected families as comparison groups and studied for 1-year periods. Occurence of acute respiratory illness was ascertained weekly by telephone and calculated as an annual rate. Persons with chronic bronchitis not only experienced more acute lower respiratory illness than healthy comparison subjects, but total illness rates were somewhat higher as well. Infection rates were determined from blood samples taken 3 times from each participant during the surveillance year. Antibody tests were performed for respiratory syncytial virus, para-influenza virus types 1, 2, and 3, influenza types A and B, coronavirus OC43, Mycoplasma pneumoniae, and Haemophilus influenzae. Differences in serologic infection rates among the subgroups of the population were similar to those seen in the clinical data, with more frequent infection among those with bronchitis than among the comparison subjects. This finding indicates that some degree of increased susceptibility to actual infection existed among those individuals with bronchitis. Influence of smoking on illness and infection rates was also examined. Infections were, in general, more frequent in smokers than in nonsmokers, but illness rates were reversed, suggesting that perception of disease differed in the 2 groups. Rates of illness and infection of other adults in the families of the index individuals with bronchitis were not influenced by the higher rates seen in the index individuals; however, it was of interest that children of persons with bronchitis did have somewhat higher rates of infection than children of comparison subjects.