The aim of this study is to determine whether some tests proposed as diagnostic of small airways obstruction (SAO) are useful in identifying the subjects at risk of developing chronic airflow limitation. Eighty five healthy male workers (46 nonsmokers and 39 smokers, aged 21-41 yrs), living in the same area and not exposed to occupational pollutants were re-examined after an interval of 6 yrs. At the first survey 39 had functional evidence of SAO as determined by the presence of one of: maximal mid-expiratory flow (MMEF) less than 65% of predicted value (pred); maximal expiratory flow when 25% forced vital capacity remains to be expired (Vmax25) less than 60% pred; closing capacity (CC) greater than 130% pred; 46 had all functional values in the normal range. We considered four subgroups: smokers and nonsmokers with and without SAO. The rate of decline in FEV1, the decline in %delta FEV1 and delta FEV1.height-3, have been evaluated and compared in the subgroups. Initial values of specific tests (MMEF, Vmax25, CC and slope of phase III) have been examined for a possible relationship with decline of FEV1. Statistical analysis of our data showed that only CC was related to FEV1 decline. However, there were no significant differences in FEV1 decline among the subgroups. We conclude that in young adult subjects functional characteristics of SAO have no predictive value for development of chronic airways obstruction.