The details of the relationship between brain function and metabolism in brain infarcts have not been studied. Using magnetoencephalography (MEG) and proton magnetic resonance spectroscopic imaging (1H MRSI), we localized sources of abnormal magnetic activities in ischemic brain regions and biochemical changes in suspected lesions showing pathological characteristics. Twelve patients with ischemic stroke were examined and the results of MEG and 1H MRSI were superimposed onto the corresponding MR images. The signal intensities of N-acetyl (NA) and lactate (Lac) were measured in the lesions with highly concentrated dipoles of slow wave activity. Eleven of 12 cases had increased slow wave activity in the cortical areas adjacent to the infarcts; 1 case was excluded because the infarct was too small (<1 cm in diameter). The signal intensity of NA in the regions with the highest slow wave activity was significantly reduced and was well correlated with the dipole density of slow waves. Though Lac was mildly accumulated in the lesions, the Lac level had no correlation with slow wave magnetic activity. The remaining and metabolically active cortical tissue showing NA signal produced the abnormal slow wave activity under lactic acidosis (mild accumulation of Lac).