The initial dose-escalating clinical trial of a novel calcium antagonist, AT877, in patients with aneurysmal subarachnoid haemorrhage is reported. AT877 is characterized by its strong spasmolytic activity, its inhibition of intracellular calcium ion activity, and the inhibition of several protein kinases. A total of 113 patients (Hunt and Hess grades I to IV) who had undergone surgery within 3 days of aneurysmal rupture entered the study. Patients were divided into 5 groups according to the total daily dose of AT877: I: 20 mg; II: 40 mg; III: 60 mg; IV: 90 mg; and V: 120-180 mg. AT877 was given by intravenous infusion over 30 min two or three times a day for 14 days after surgery. Although AT877 did not completely abolish angiographic vasospasm, severe vasospasm was seen less frequently in patients given higher doses. Vasospasm was the cause of a poor clinical outcome (Glasgow outcome scale rating 3 or greater) in 19%, 7%, 9%, 8%, and 6% of the patients in groups I to V, respectively. The results indicated a favourable clinical effect of AT877 at doses above 40 mg per day. Only mild hypotension was seen, even when 60 mg of AT877 was infused over 30 min. AT877 appears to be effective in patients with subarachnoid haemorrhage. Part of its effect may be attributable to protection of the brain from ischaemic insults due to chronic cerebral vasospasm. However, the drug still needs to be evaluated in a placebo-controlled double-blind trial (which is currently being carried out).