To assess the value of transcranial Doppler examination for the early prognosis of ischemic stroke, we examined 24 patients (15 males and 9 females, mean age 66.8 +/- 9.3 years) with hemispheric cerebral infarction, within 6 hours of stroke onset. Of these 24 patients, 22 were evaluated on the Canadian Neurological Scale, the Toronto Stroke Scale, and the Barthel Index on days 60 and 120. Mean flow velocity in the middle cerebral artery on the lesion side was measured and values outside the range 30 to 80 cm/sec were rated abnormal. Two of nine patients with normal flow velocity died compared to five of the 13 patients with abnormal values. Four of the seven remaining patients in the former group made a full recovery compared with none of the remaining eight patients in the latter group (P less than 0.05). Neurological and functional status measured on the scales used on days 60 and 120 were also significantly better in the group with normal flow velocity. Early transcranial Doppler may prove useful in predicting the outcome of hemispheric infarction in the acute phase of cerebral ischemia.