The prognostic significance of admission leukocytosis with respect to ischemic complications of subarachnoid hemorrhage was retrospectively investigated in a series of patients with recently ruptured intracranial aneurysms. The present study concerned 47 consecutive cases admitted within 72 hours following the last hemorrhage, in the years 1982-1984. There was no difference in the admission WBC counts between patients who subsequently deteriorated due to ischemic complications and those who did not. However, the cell count rose significantly at the time of the clinical manifestations of ischemia, possibly as a result of structural damage of brain tissue and/or increased sympathetic and adrenocortical activity. The possible contribution of leukocytes to the pathogenesis of ischemic damage following subarachnoid hemorrhage--perhaps through the release of leukotrienes--will require further investigation.