The relationship of maximal oxygen uptake with tobacco consumption was investigated in sixty-one young males. There was a significant negative correlation between daily consumption of tobacco and measured maximal oxygen uptake (Vo2max) expressed relative to body weight (r = -0.368, P less than 0.01) and to lean body mass (r = -0.497, P less than 0.001), respectively. No correlation could be demonstrated with regard to predicted maximal oxygen uptake (Vo3maxp). No difference was demonstrated between Vo2maxp and Vo2max in nonsmokers and heavy smokers, whereas Vo2maxp was significantly higher (P less than 0.01) in the group of moderate smokers than Vo2max. It is concluded that tobacco smoking decreases Vo2max even in young moderate smokers. Smoking habits should be considered among factors affecting Vo2maxp from cardiac frequency at submaximal levels.