A screening for coronary risk factors in 18 000 Oslo men yielded 16 525 "healthy" men, aged 20-49. The intercorrelation of serum cholesterol, body weight and cigarette smoking was found to be more pronounced than described in other studies. Increasing daily exposure to cigarette smoke in the order: never-smoker, ex-smoker, non-inhaling smoker, inhaling smoker and present non-filter smoker, was parallelled by increasing cholesterol levels, but not by increasing body weight. Daily cigarette-smokers had lower body weight and higher serum cholesterol values than never-cigarette-smokers, with the exception of the 20+ cigarette-smokers who had higher serum cholesterol values and body weight than the never-cigarette-smokers. As regards ex-cigarette-smokers, both body weight and serum cholesterol tended to increase with the number of cigarettes smoked before quitting. Possible explanations of these findings are discussed.