Eighty-four healthy asymptomatic sedentary smokers and 92 healthy sedentary non-smokers of the age range 20-59 years were investigated for their maximum oxygen uptake capacity (VO2max) and related cardiorespiratory parameters at the level of maximal exercise by bicycle ergometry. The subjects were blocked into four age decades of 20-29, 30-39, 40-49, and 50-59 years to show the effect of smoking on VO2max of smokes of different age groups. The physical characteristics of smokers and non-smokers of comparable age groups did not show any significant difference. The smokers of each subsequent age group consumed 5.9 +/- 4.1, 6.3 +/- 5.7, 12.7 +/- 7.1, and 11.5 +/- 9.1 pack years of cigarettes, respectively (pack year = number of packets of cigarettes per day X number of years of smoking). VO2max of smokers (38.9 +/- 4.6 ml.kg-1.min-1) was significantly lower (p less than 0.05) than that of nonsmokers (42.1 +/- 3.2 ml.kg-1.min-1) only in the young age group of 20-29 years. VO2max expressed in per kg of the body weight (VO2max/BW) was found to be significantly (p less than 0.01) and negatively correlated with number of cigarettes smoked per day (-0.36, p less than 0.01), number of years through which smoked (-0.38, p less than 0.01), and pack years (-0.42, p less than 0.01). In other age groups, though non-smokers predominated over smokers in VO2max, the differences were not statistically significant. Also, in these age groups, smoking histories failed to reveal any significant correlation with VO2max. This suggests that smoking impairs VO2max only in the young ages. By increasing age, VO2max was diminished by 13% from 20 to 59 years in non-smokers and 15.5% from 20 to 59 years in smokers. Age also diminished HRmax and VEmax of smokers in the same manner as in the case of non-smokers. The VO2max of Indian sedentary non-smokers was found to be lower than those of Caucasians, Kurds, Yemenites, Europeans, and Africans. Values reported on Asians were found to be comparable with those of the present study.