The tandem pace of medical knowledge and prevention of ischaemic heart disease over the past 50 years is testimony to the effectiveness of a combination of massive scientific research, continuous transfer of the results to medical practice, community actions and population aware ness. The death rate from coronary heart disease in the United States rose 20% from 1950 to 1963, when a dramatic and steady downward inflection began, arriving today at a rate over 50% lower. Numerous factors have contributed to this success. By 1950 lipoproteins had just been discovered, but a decade later a great surge in research had focussed upon plasma cholesterol and lipoprotein concentrations as major predictors of risk. Today, a continuing expansion and sophistica tion of that research has removed all doubt about the significance of particular patterns. The pathway to ideal prophylaxis, however, particu larly for risks associated with inherited lipoprotein disorders, still awaits the untangling of great amounts of new information that continue to rise from application of molecular technology. This volume deals with many of the contemporary puzzles. One theme revolves about the high density lipoproteins. For twenty years the HDL have been considered a defence against the caprices of the LDL, now believed to be particularly villainous after oxidation.