Persons from 148 randomly selected households in an urban community were screened in their homes using a modified British Medical Research Council respiratory disease questionnaire and a portable spirometer. Analysis showed a significant tendency for chronic bronchitis to aggregate within households. Significant aggregation was observed for 1-sec forced expiratory volume, when measured as the per cent of the predicted value or as a score calculated from the data. The 1-sec forced expiratory volume was significantly correlated between siblings, but less clearly so between spouses. Correlation of 1-sec forced expiratory volume between mother and child appeared to be confounded by maternal smoking habits, an effect most notable between mothers and male offspring. The 1-sec forced expiratory volume of fathers was significantly correlated with that of their children, especially female children, an effect that appeared to be independent of smoking habits.