The results of a respiratory questionnaire and spirometric tests of 133 ex-smokers out of 649 male public servants aged 15--64 years have been analysed. When the population was adjusted for age, height and the presence or absence of chronic respiratory symptoms the FEV1 of the ex-smokers had not returned to normal but fell between that of the light (less than 10 a day) and moderate cigarette smokers. Factors contributing to this have been investigated. Factors affecting the FEV1 of the ex-smokers were found to include duration of smoking, quantum smoked and years since smoking ceased. An interactive effect has been demonstrated between quantum smoked and duration of smoking such that ex-smokers who used to smoke 10 or more cigarettes a day for more than 10 years had the lowest lung function but duration of smoking was not important if less than 10 cigarettes a day had been smoked. Only just over a third of the ex-smokers gave health related reasons for giving up smoking, a proportion which is considerably lower than has been found in other studies. Possible reasons for this difference are discussed. As in other studies less than 10 percent gave up smoking because of its cost. Respiratory screening to include questions on cough, phlegm and wheeze together with measurement of the FEV1 is an important way of demonstrating to individual smokers evidence of any damage caused by their smoking.