The smoking habits in patients with atherosclerosis in the lower limbs and the effect of advising them to stop smoking was studied by means of self-declaration of the number of cigarettes smoked per day and determination of serum thiocyanate. Ninety-six per cent of males and 70 per cent of the females were smokers or ex-smokers. The number of years of smoking was about 40 for the smokers of both sexes and the male ex-smokers and 23 for the female ex-smokers. The number of cigarettes smoked per day reported by the patients was less than that reported by the smokers in a reference population. The serum thiocyanate levels confirmed the smoking status of the non-smokers and showed that about one-sixth of the ex-smokers had smoked in the last month prior to the study, and that the smokers on the average were heavy smokers smoking much more than the self-reported number of cigarettes. The effect of advising the patients to quit smoking was very disappointing. A maximum of 15 per cent of the smokers stopped smoking while some of the ex-smokers resumed smoking.