Cerebral blood flow (CBF) was measured by xenon-133 inhalation and single photon emission computerized tomography (SPECT) in 7 patients with acute cerebral ischaemia prior to and 30 min after intravenous infusion of nimodipine (1 mg). Neurological examination, CT and CBF study were performed no later than 6 h after the onset of symptoms. Regional perfusion abnormalities were seen in all patients when the CT scan was still normal. Follow-up CT revealed low-density areas roughly corresponding to the core of the perfusion defect. Nimodipine infusion significantly decreased the mean arterial blood pressure (P less than 0.01), while PaCO2 and clinical symptoms remained unchanged. A significant CBF improvement (P less than 0.05) after nimodipine was seen in the border zone of the ischaemic infarct but not in the core of the lesion or in the unaffected contralateral hemisphere.