Reduced serum levels of folic acid, vitamin B12 and elevated homocysteine levels are could be related to the aetiology of atherosclerosis, coronary heart disease and cercbrovascular strokes.In this study, the relations between plasma levels of thrombin-antithrombin complexes (TAT), prothrombin fragments 1,2 (F1+2) and plasma levels of folate, vitamin B12 and homocysteine (Hcy) were investigated in 25 cases with acute myocardial infarction,25 cases with acute cerebrovacular stroke(in absence of classical risk factors for atherosclerosis) as well as25 normal healthy subjects. Plasma levels of TAT, F1, 2 and Hcy were significantly higher in both patients groups compared to control subjects, whereas plasma folate levels were significantly lower in these cases as compared to control group. Moreover, vitamin B12 plasma levels showed insignificant changes among the studied groups. Furthermore, plasma TAT and F1,2 exhibited significant positive correlations with Hcy plasma level and a significant negative correlation with plasma folate levels in both patients , groups, also folate levels were significantly negative in relation to Hcy among patients , groups.These data confirm that for myocardial infarction and stroke patients there is a significant activation of blood coagulation system as well as increased risk for atherogenesis that are adversely influenced by the elevated plasma Hcy and the reduced plasma folate levels. These results may have therapeutic implications.