In 1974 Blackburn wrote: "The present state of progress in cardiovascular epidemiology includes the overriding demonstration that there are vast differences in the frequency of coronary heart disease (CHD) among populations and that the risk of the diseases varies enormously according to the burden of individual or population risk characteristics .... The thrust will surely continue towards quantitative rather than qualitative assessment of CHD risk and a preventive approach to its management. The practitioner will no longer regard the multiple mild and moderate risk factors and bad habits as trivialities, but as powerful combined elements of risk requiring effective action ... Prevention is still the word; it should now be given its balanced share of effort which, I hope we can now agree, involves more than just lip service". These and other statements can be found in a detailed literature review given in chapter II. In order to provide more than just "lip service" in 1971 at the Occupational Health Service for the Port of Rotterdam a standardized screening effort was undertaken to investigate the prevalence of CVD among dockworkers between the ages of 55 and 65. The results of the first screening have been published by Baart in 1973. A second screening in the same group of dockworkers was carried out between October 1972 and November 1973. In addition the possibilities of intervention in individuals with abnormal findings were to be explored. These investigations provide the basis for this thesis. A total of 503 persons studied at screening I were invited to participate in screening II. Four hundred and fortyseven of them appeared. The screening consisted of various items of the medical history obtained by means of a standardized questionnaire, the determination of height, weight, blood pressure, a resting· and an exercise-electrocardiogram, a chest roentgenogram and the determination of serum cholesterol, total lipids, blood sedimentation rate as well as data on ventilatory functions. The methodology and patient material is described in chapter III and in various annexes. The follow-up study provided not only data on the prevalence of risk indicators at two different times but it also gave the opportunity to evaluate the consistency of the testing procedures employed during the investigations