Succinylcholine-induced hyperkalemia has been reported to occur in many neurological disorders including subarachnoid hemorrhage. The purpose of this study was to compare the effect of succinylcholine on serum potassium levels in patients with ruptured cerebral aneurysms undergoing either early (less than or equal to 4 days; n = 14) or delayed (5-16 days; n = 20) surgery. Thirty-four patients were classified according to the number of days from subarachnoid hemorrhage to surgery. Arterial serum potassium levels were measured after induction of anesthesia but before succinylcholine, and 1, 5, and 10 min after the administration of succinylcholine. The electrocardiogram was continuously monitored. The mean ( +/- SD) increase in serum potassium level of 0.4 +/- 0.2 mmol/L occurred at 10 min but was not statistically significant, nor was there any statistically significant difference in serum potassium levels related to time between subarachnoid hemorrhage and administration of succinylcholine. We found no evidence of succinylcholine-induced hyperkalemia in patients undergoing either early or delayed cerebral aneurysm surgery.