One hundred fifty subjects were enrolled in a long-term study of obstructive lung diseases; 84 of these were subjected to five or more spirometric studies over a period of two or more years. Stepdown regression analysis was performed to determine the association between many different variables and the annual rates of change in the forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1). The following associations were noted to be significant (p less than 0.03); more favorable rates of change of the FVC and FEV1 were associated with a higher alpha1-antitrypsin level and older age. Less favorable changes were associated with more years of cigarette smoking, more airway reactivity and more frequent lower respiratory tract illnesses.