The acute and chronic effects of cigarette smoking on selected physiological responses were determined in seven well-trained non-smokers and seven well-trained habitual smokers. Non-smokers and smokers did not differ significantly with respect to maximal oxygen consumption (VO2max). The acute effect of smoking two cigarettes immediately prior to a graded exercise stress test on a treadmill ergometer did not significantly alter the VO2max of either group. However, the time taken for non-smokers to reach exhaustion decreased significantly (F = 5.381, P less than 0.05) by a mean of 0.64 min. Smokers recorded lower scores for forced vital capacity (FVC) and forced expiratory volume in the 1st s exhalation (FEV1) than non-smokers. Only the mean FVC of smokers recorded 5 min post-exercise was significantly altered by pre-exercise smoking. No differences were found between the resting heart rates (HR) of non-smokers and smokers. Smoking two cigarettes significantly (F = 44.720, P less than 0.01) increased the mean resting HR of smokers and non-smokers by 15.8 beats X min-1 and 15.6 beats X min-1 respectively. No alteration to the exercise HR of either group was found under smoking conditions of the VO2max tests.