Whether succinylcholine causes an increase in intracranial pressure (ICP) in patients with brain lesions is uncertain and, if increased ICP does occur, its pathophysiology remains unknown. The authors investigated both the effect of succinylcholine on ICP and its modification with prior neuromuscular blockade by measuring ICP (subarachnoid bolt) in 13 consecutive patients with brain tumors who received succinylcholine both before and after complete neuromuscular blockade with vecuronium. Anesthesia was induced with thiopental, 6 mg X kg-1 iv, and nitrous oxide, 70% in oxygen, while ventilation was controlled (PaCO2 = 37.2 mmHg +/- 1.7 SE). Succinylcholine, 1 mg X kg-1 iv, was administered and ICP, heart rate (HR), and blood pressure (BP) were recorded until normal twitch tension was restored. Complete neuromuscular blockade was then established with vecuronium, 0.14 mg X kg-1 iv; 3 min later, succinylcholine, 1 mg X kg-1 iv, was repeated. The resulting changes in ICP, HR, and BP were recorded for 3 min. Following the first dose of succinylcholine, mean ICP increased from 15.2 mmHg +/- 1.3 SE to 20.1 mmHg +/- 2.0 SE (P less than 0.05), with five of the patients sustaining increases in ICP of 9 mmHg or greater. In contrast, when succinylcholine was given after vecuronium-induced paralysis, no patient developed an increase in ICP greater than 3 mmHg (P less than 0.05 compared with the incidence of ICP greater than or equal to 9 mmHg observed after the first dose of succinylcholine). A second group of six patients received two doses of succinylcholine according to the same protocol but without an intervening dose of vecuronium.(ABSTRACT TRUNCATED AT 250 WORDS)