Regional cerebral blood flow, oxygen consumption, blood volume and glucose metabolism were studied by positron emission tomography (PET) in 16 patients with striato-capsular infarction during the acute phase. Visual evaluation of tomograms and quantitative analysis of PET data detected in all patients severe flow disturbances and metabolic derangement within the territory of the penetrating branches of the middle cerebral artery. Additionally remote effects were observed. The correspondence of early PET changes with the diagnosis of striato-capsular infarction was verified later on by computerized three-dimensional alignment of PET scans and MRI. These results demonstrate that PET allows localization of small striato-capsular infarction with high accuracy in the acute phase by demonstrating both severe local flow disturbances and metabolic derangement, as well as remote effects.