Forty patients with past history myocardial infarction were divided into three groups. Group I served as controls, while Groups II and III were given respectively, 1 g and 2 g vitamin C daily, divided in two doses. Samples were collected initially, and then every 2 months during the 6-month period of vitamin C administration and finally 2 months after stopping vitamin C. Vitamin C, 0.5 g twice daily (Group II), increased serum ascorbic acid by about 22% (P less than 0.05). However, no significant changes were observed in fibrinolytic activity or blood lipids. When the dose of vitamin C was doubled, serum ascorbic acid increased by about 96% and fibrinolytic activity increased by 45% (P less than 0.01), while the platelet adhesive index decreased by 27% (P less than 0.01). The serum cholesterol level dropped by 12% (P less than 0.05) and a significant decrease in serum beta lipoproteins and an increase in the alpha fraction was also seen. A further 40 patients with acute myocardial infarction were divided into two groups; one received 2 g vitamin C daily for the first 20 days and the other received a placebo. Blood samples were collected every 10th day during the 40-day follow up. Vitamin C administration increased fibrinolytic activity by 62.5%, while serum ascorbic acid rose by 94%.