Potential cerebrospinal fluid (CSF) markers for Alzheimer's disease (AD) include tau protein, the 42 amino-acid form of amyloid beta (amyloid beta(1-42)) and apolipoprotein E (apoE). To study new aspects of these protein markers, we examined consecutive CSF samples from 26 patients with acute ischemic stroke. CSF samples were taken on day 0-1, day 2-3, day 7-9, 3 weeks and 3-5 months after the stroke. CSF-tau showed a marked increase day 2-3, which peaked after 1 week and returned to normal after 3-5 months. CSF-tau also showed correlation (r=0.95; p<0.01) with the size of the infarct. In contrast, CSF-amyloid beta(1-42) and CSF-apoE showed no significant changes during the period. The marked increase in CSF-tau levels after acute ischemic stroke indicate that CSF-tau reflect the degree of neuronal damage. The reason for unchanged levels of CSF-amyloid beta(1-42) and CSF-apoE after ischemic stroke remains unclear.