The results of a Phase II clinical trial of intrathecal recombinant tissue-type plasminogen activator for the prevention of vasospasm were reported. The subjects were 53 patients with aneurysmal subarachnoid hemorrhage (SAH), Groups 2 to 4 in Fisher's preoperative computed tomography classification and Grades II to IV in the Hunt-Kosnik classification. Twenty-four hours after surgery, tissue-type plasminogen activator (TD-2061) was intracisternally administered via a catheter (0.1, 0.2, or 0.4 mg, three times daily for 5 days). The clot-dissolving effects assessed as "effective" and "markedly effective" were virtually the same in the 0.1- and 0.2-mg groups (66.7% and 64.3%, respectively) but slightly lower (53.3%) in the 0.4-mg group, suggesting an adequate effect in the 0.1- and 0.2-mg groups. Severe angiographic vasospasm was not observed in any of three groups. No intergroup differences were noted in the incidence of symptomatic vasospasm, low density on computed tomography 1 month after SAH, and functional prognosis. Bleeding complications were noted in 4 patients (7.5%), including 1 case of SAH in the low 0.1-mg group, 2 cases of SAH in the 0.2-mg group, and 1 case of epidural hematoma in the 0.4-mg group. In overall safety rating, 3 cases with increased SAH and 1 case of epidural hematoma were assessed as "safety doubtful." Other minor side effects such as headache and hepatic dysfunction attributed to the effect of other simultaneously used drugs were assessed as "almost safe," and the rate of "almost safe" and "better" for all dose groups was about 90%, suggesting a safe dose level for all groups. These results suggest that repeated intrathecal administration of tissue-type plasminogen activator is useful for preventing vasospasm even in the low dose of 0.1 mg.