Hyperhomocysteinemia is an independent risk factor for atherothrombotic cerebral stroke. Vitamin B-12 and folic acid are important determinants of homocysteine metabolism. We aimed to evaluate the relationship, if present, between vitamin B-12 and folic acid levels and acute cerebral stroke in this study. Blood aliquots drawn within 24 hours after the stroke from hospitalized patients (n=66) with the diagnosis of acute ischemic cerebrovascular episode and also blood samples from 38 healthy controls without any vascular risk factor were analyzed. With a competitive, chemoluminescence assay, serum levels of vitamin B-12 and folic acid were measured in blood samples taken within 24 hours after the stroke. The differences and correlations were tested using frequency test, student-t test and multivariate analysis. Mean serum vitamin B-12 levels were significantly lower in the patients than in the control subjects, 245.40 (S.D.: 72.9) and 343.2 (S.D.: 113.0) pg/ml respectively (p=0.0001). This difference was independent from other risk factors. Likewise, mean serum folic acid levels were lower in the patients than in the control subjects, 4.62 (S.D.: 1.94) and 5.97 (S.D.: 1.19) ng/ml, respectively (p=0.003). Mean serum levels of vitamin B-12 and folate at the convalescence phase were 253.05 (S.D.: 68.78) pg/ml and 4.48 (S.D.: 2.08) ng/ml, respectively; the values obtained at the acute phase were not significantly different from the values obtained at the convalescence phase. We conclude that low vitamin B-12 and folic acid concentrations are associated with an increased risk of stroke, and the relationship for vitamin B-12 is independent from the other known modifiable stroke risk factors. For understanding the effects of B-12 and folate in stroke patients, more detailed follow-up studies with long period are needed. (C) 2004 Tohoku University Medical Press.