Résumé : Results are presented from the Belgian Heart Disease Prevention Project, part of the WHO European Collaborative Trial in the Multifactorial Prevention of Coronary Heart Disease (CHD). 19 409 men aged 40-59 yr took part; they were employed in thirty factories which formed the allocation units for a randomised controlled trial lasting 5-6 yr. The intervention package consisted largely of health education promoting a cholesterol-lowering diet, smoking cessation, weight control, physical activity, and treatment of arterial hypertension. A programme of information was supplemented by face-to-face counselling at the workplace by two physicians attached to the project. The coronary risk profile was reduced in the intervention group, compared with that in the control group, especially during the first 4 yr, by effects on serum cholesterol, number of cigarettes smoked daily, and arterial blood-pressure. Total mortality was 17.5% lower in the intervention group than in the control group (p = 0.038). Coronary mortality was reduced by a non-significant 20.8% whereas CHD incidence (non-fatal myocardial infarction plus fatal myocardial infarction plus sudden deaths) was reduced by 24.5% (p = 0.031). Non-fatal myocardial infarction (not a major end-point) was similarly reduced by 26.1% (p = 0.030).