Subarachnoid haemorrhage due to a ruptured cerebral aneurysm is a dramatic event in neurosurgery and one of the most destructive. Its management is complicated by the risks of rebleeding and cerebral vasospasm and their sequelae. Rebleeding and vasospasm rarely occur before three days after the primary bleed.'2 Angiographic vasospasm is seen most often 10 to 17 days after bleeding.3 Because of the brain's vulnerability during spasm many surgeons prefer to wait until two weeks after the primary bleed to obliterate the aneurysm.4 Sano and Saito5 reported fatal postoperative vasospasm in patients operated upon on days 4 and 7 after a haemorrhage. However, the 'spasm period' coincides with the time when rebleeding is most likely. The incidence of rebleeding is highest at the end of the first week and at the beginning of the second after the primary bleed, and the mortality after the first recurrence is reported to be between 43 % and 64 %. 6 Thus most surgeons accept spontaneous mortality due to either progressive deterioration or to rebleeding during the first and second week. The surgical mortality when the patient has recovered from this deterioration can be low. It is therefore necessary to look for ways of lessening the risk of rebleeding during the first critical two weeks.The aim in treating patients with a ruptured aneurysm with antifibrinolytic agents is to prolong the duration of the formed blood clot within and about the wall of the aneurysm and thus prepare the way for mechanical repair of the rupture. Promising results with aminocaproic acid (EACA)7-11 and AMCA12-19 have been reported. Others, however, found that these drugs had no effect on rebleedings.20-24 In this paper I report the results of two controlled clinical trials of the effect of AMCA on aneurysmal rebleeding, vasospasm, hydrocephalus, and circulatory disturbances. Patients and methodsThe trials were conducted over the years 1972 to 1978. The sealed-envelope technique was used instead of the double-blind method, since it was considered unethical to give placebo injections for a prolonged period. Only patients admitted to the hospital within three days after a subarachnoid haemorrhage due to a ruptured aneurysm and in whom treatment was started within 72 hours were included in the trials. The diagnosis was verified by spinal fluid (CSF) examination and cerebral angiography. In the second series all patients were also examined with CT-scan.The patients were randomly assigned to conservative treatment (bedrest and sedation) or conservative treatment together with the administration of AMCA. In a first series of 46 patients 23 were given AMCA by slow intravenous injection in a dosage of 1 g 4-hourly during the first week, 1 g 6-hourly during the second to fifth weeks inclusive, and 1 g 8-hourly during the sixth week. In a second series of 59 patients 30 received AMCA in hourly intravenous infusions 6 g daily during the first week, 4 g daily during the second week, and 1 5 g by mouth four times a day during the third to sixth weeks. The patient...