The effect of high dose nicardipine on delayed cerebral vasospasm was studied in 33 patients with aneurysmal subarachnoid hemorrhage (SAH). Intravenous infusion of nicardipine started before or immediately after early operation. The dosage was from 4 to 10 mg/h with an average of 7.4 mg/h. The duration was from 2 to 17 days with an average of 12.3 days. Symptomatic vasospasm was observed in only one (3%) out of 33 patients. The remaining 32 patients (97%) showed neither ischemic symptoms nor low-density areas on computed tomography. Severe angiographical vasospasm was diagnosed in 3 patients, who entered hospital on day 3 to 5 after initial attacks. They were operated upon on day 4 to 6 under the administration of nicardipine before or immediately after the operation. No patients showed symptomatic vasospasm and angiographical vasospasm was improved markedly. The present study demonstrated that high dose nicardipine appeared to prevent both brain ischemia and angiographical vasospasm after aneurysmal SAH.