The clinical trials and angiographic studies of cholesterol lowering have been of decisive importance in persuading scientific and public opinion that elevated serum cholesterol is a causal element in the chain of events leading to CHD and that treatment by diet and drugs is effective in lowering the risk of CHD. The appropriateness of these opinions is well illustrated by the analyses of the combined trials, which show that the clinical event rate can be lowered by about 20% if cholesterol levels are lowered by 10%. The reduced risk for CHD applies to both primary and secondary prevention. Further, the angiographic studies have now demonstrated that vigorous lipid-lowering therapy leads to improvements in the angiographic appearance of coronary vessels, which are accompanied by large reductions in CHD risk. Diet and a variety of drugs appear to modify the risk of CHD. The results of studies using combinations of drugs, for example, bile acid-binding resins with either niacin or hydroxymethylglutaryl coenzyme A reductase inhibitors, are particularly impressive. The primary purpose of treatment remains the reduction of total and LDL cholesterol; however, the possibility of an additional benefit from improving other aspects of the lipid profile (such as raising HDL cholesterol levels) at the same time should not be ignored. In many instances, combinations of drugs are needed to achieve optimal lowering of serum cholesterol or to treat all elements of the disorder. Although the treatment of high-risk but apparently healthy individuals should not be neglected, it would be particularly appropriate to institute intensive diet and combination drug therapy in patients with existing CHD, in view of their high risk of reinfarction if left untreated. The secondary prevention trials provide evidence that clinical events can be reduced in such patients. The angiographic studies strongly suggest that large reductions in cholesterol to much lower levels (in-treatment LDL cholesterol levels below 100 mg/dL were frequently observed) than those achieved in the secondary prevention trials markedly reduce the rate of coronary events in patients with existing disease.