To examine the influence of atrial fibrillation (Af) on stroke onset, we measured the plasma D-dimer level, thrombin antithrombin III complex and plasmin alpha 2 antiplasmin complex (PAP) in 46 stroke patients with Af and 87 stroke patients without Af. These marker levels were significantly higher in Af patients with stroke than in those without stroke (n = 16), and thus do not seem to be affected by Af alone. Abnormal values were also more frequent in acute Af stroke patients with visible occlusion of the major cerebral artery than in those without Af. The D-dimer and PAP levels in all Af stroke patients in the younger-aged patients (< or = 64 years) were significantly higher than those without Af, but not noted in the older-aged group (> or = 75 years). These results suggest that the D-dimer and PAP levels in younger-aged patients with Af indicate the existence of cerebral emboli due to Af.