Twenty-five patients with expansive pathologic brain lesions, who were anesthetized with thiopental, nitrous oxide in oxygen, and fentanyl, and who were mechanically ventilated to ensure normocarbia, received atracurium besylate 0.6 mg/kg, intravenously. Intracranial pressure, mean arterial pressure, central venous pressure, heart rate, and end-tidal CO2 were simultaneously recorded for 5 min before and for 10 min after administration of the muscle relaxant. No statistically significant changes were observed after administration of atracurium besylate. These results suggest that atracurium besylate may be used for muscle relaxation during neurosurgical operations, despite its potential for histamine release and excitement of the central nervous system.