In an ongoing study 558 consecutive survivors of myocardial infarction below 70 years, mean age 59 years, were randomly allocated 4 months after the acute episode into a control group or a chemotherapy group from December 1972 to April 1976. Both groups were given moderate advice about diet and the chemotherapy group was prescribed clofibrate, 1 g twice daily, and nicotinic acid 1 g three times daily. Serum cholesterol and triglycerides were lowered around 15-20% and 30% respectively in the chemotherapy group while only insignificant reductions were observed in the control group. Until December 1976 total mortality and mortality from IHD has been the same in the two groups. The number of non-fatal myocardial infarctions has been 38 in the control and 19 in the chemotherapy group, a statistically significant reduction (P less than 0.01).