Smoking has for some time been strongly sus pected of being a major aetiological factor in chronic bronchitis. Confirmatory evidence has accrued from many epidemiological studies involving widely different populations. Abbott, Hopkins, Van Fleit, and Robinson (1953) found that, in 294 hospital patients with emphysema and cough, tobacco smoking could be incriminated as an aetiological factor in about two-thirds of cases, and Palmer (1954) confirmed these findings, again on a hospital population. The use of hospital populations in epidemiological studies is open to danger of selection, with consequent doubts about general applicability of results, but work of Abbott and Palmer and their collaborators cited above has been confirmed in studies of representative samples of general population. Clifton (1956), in a study of rural dwellers and of workers in heavy industry in Sheffield, found smoking to be an important factor in prevalence of chronic bronchitis in these two populations. Ogilvie and Newell (1957), in their Newcastle survey, confirmed association be tween smoking and chronic bronchitis, but were unable to relate prevalence of disease to amount of tobacco smoked. Brown, McKeown, and Whitfield (1957), in a study of 1,062 men aged 60-69 years, and Higgins, Oldham, Cochrane, and Gilson (1956), in their Leigh survey, agreed with these findings. Less information is available about effects of smoking on ventilatory function. Franklin (1958) found that heavy smokers recorded lower flow rates in maximal forced expirations than did light smokers and non-smokers, this happening frequently in absence of any pulmonary abnormality. Eich, Gilbert, and Auchincloss (1957), investigating experimentally effects of cigarette smoking, found, in emphyse matous patients, that there was an increase in air ways resistance after smoking one cigarette, but Bickerman and Barach (1954) found significant effect after their subjects had smoked three cigarettes. Higgins (1959), in a study of 734 men aged 25 to 64 years randomly selected from urban and rural populations, recorded a higher indirect maximum breathing capacity (M.B.C.) for non-smokers than for smokers, but found no significant downward trend with increasing tobacco consumption among smokers. Fletcher, Elmes, Fairbairn, and Wood (1959) came to same conclusion about a group of London postmen, aged 40 to 59 years. However, Higgins, in a study with other workers of a popula tion of mixed occupations in Staveley, Derbyshire, found that the heavier smokers recorded a lower mean M.B.C. than lighter (Higgins, Cochrane Gilson, and Wood, 1959). As part of National Coal Board's Pneumo coniosis Field Research (Fay, 1957; Fay and Rae, 1959; Rogan, Ashford, Chapman, Duffield, Fay, and Rae, 1961), periodic medical surveys, including measurement of ventilatory function and physique and assessment of radiological pneumoconiosis, respiratory symptoms, and smoking habits, are car ried out on underground and surface workers at a sample of 25 collieries distributed throughout main British coalfields. The data collected on these surveys provide a convenient opportunity to examine relation between smoking habits and these other factors in complete working populations, and this paper is concerned with results obtained at first three collieries in Scotland at which necessary measurements have been made. 106