compare male smokers and non-smokers could not detect a significant difference in PEF, MEF, and Tiffeneaux index over the various exposure categories (χ2 test) or as a total group (ANOVA). Again a reverse trend was found towards more obstruction in non-smokers for all variables. The percentage obstruction as defined by an FD 15 Hz resulted in 2% obstructive people, which increased to 6% when lowering the f0 criterion for obstruction to 13 Hz.Suprisingly,less cases with obstruction were found in smokers (5.8%) than among non-smokers (7.7%) although the difference was small and not significant.It was also noticed that the frequency dependency criterion (FD