Acute cerebral ischemia triggers interleukin-6 (IL-6) release into cerebrospinal fluid and blood. IL-6 induces synthesis of the acute phase proteins (APPs) in the liver. Higher blood IL-6 level in stroke patients is associated with larger infarct size, greater neurological deficit on admission, early neurological worsening, and increased risk of death or poor functional outcome. The level of C-reactive protein (CRP), the major APP in man, rises in blood during acute stroke reaching maximal values between 5 and 7 day after stroke onset. Elevated CRP level in acute ischemic stroke predicts unfavorable outcome and is associated with increased risk of recurrent stroke or other cardiovascular events. Increased level of fibrinogen, another APP, is associated with worse outcome in patients with ischemic stroke. The acute phase reaction accompanies also intracerebral hemorrhage. Serum IL-6 and CRP level increases in the first days after intracerebral hemorrhage. Plasma IL-6 is independently associated with hematoma enlargement and fibrinogen level predicts early neurological deterioration and outcome in patients with intracerebral hemorrhage.