The data from a longitudinal population study in Tucson, Arizona, were used to evaluate the effects of acute lower respiratory illnesses on pulmonary function in subjects over 25 years of age. In five of nine surveys performed during the first 13 years of follow-up (1972-1985), similar questions were asked concerning chest colds occurring in the past few years. There were 1,151 men and 1,473 women who had questionnaire and spirometric data collected in at least one of these surveys. The random effects longitudinal model with first-order autoregressive error structure was used in the analysis of changes in pulmonary function after the acute illness episode, adjusted for the effects of age, height, cigarette smoking, and chronic respiratory diseases. The analyses indicated that pulmonary function is reduced for several years after a single chest cold in men and after multiple chest colds in women. After an episode of pneumonia, pulmonary flow indices were reduced, with lower values sometimes persisting for several years.