Three serial spirometric determinations of forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV1.0) were performed during a 10-yr period for 268 adult male cigarette smokers, 181 quitters, and 254 who had never smoked. Smokers were further divided into high- and low-tar consumption groups. Spirometric data were analyzed by repeated measures analyses of variance using time (aging) and smoking status as independent variables and age as a covariate. Results indicated that FVC and FEV1.0 were relatd to smoking status. For all age groups, nonsmokers performed best on spirometry, while current smokers performed worst. The decline in FEV1.0 over time was greatest in current smokers, especially the high-tar group. Loss of FVC over time was not influenced by smoking status.