The electrocardiograms (ECG) of 232 male non-smokers and 224 male smokers, aged 20-60 years, devoid of cardiovascular diseases, were studied. Among these subjects 5.2% of non-smokers and 6.7% of smokers had pathological ECGs. Non-pathological ECGs of 220 non-smokers and 209 smokers were analyzed for R, S and T-wave amplitudes, P and QRS axes and P-R, QRS and Q-Tc intervals. The 2 groups did not differ significantly from each other for R and T-wave amplitudes in any of the age groups except for 40-60 years, in which R-amplitude obtained from standard limb leads was significantly lower in smokers. S-amplitude recorded from standard limb leads was significantly lower in smokers of all ages combined. The reverse phenomenon was noted for S-amplitude obtained from precordial leads. R, S and T-amplitudes decreased with the advancement of age at a relatively higher rate in smokers. These waves had significant negative correlation with pack years of smoking habit. QRS and P axes differed significantly between smokers and non-smokers. The rate of shifting of these axes to the left with increasing age was relatively higher in non-smokers. Lung function did not show any relation to electrocardiogram in normal healthy subjects. These results indicate that aging affects electrocardiographic wave patterns and that this aging effect is modified by long term smoking.