In order to examine the effects of verapamil on intracranial pressure (ICP) in patients with compromised intracranial compliance, five hypertensive patients with supratentorial tumors were given verapamil, 5 mg intravenously, at the time of anesthesia induction. Within 4 minutes, ICP increased 67% from 18 ± 4 mm Hg (standard error) to 27 ± 5 mm Hg (p < 0.05), whereas mean arterial pressure decreased 20% from 111 ± 7 mm Hg to 89 ± 4 mm Hg (p < 0.05), and cerebral perfusion pressure (CPP) decreased 33% from 93 ± 11 mm Hg to 62 ± 6 mm Hg (p < 0.05). The increases in ICP responded promptly to hyperventilation and intravenous lidocaine (1.5 mg/kg). A control group of five hypertensive patients with supratentorial tumors received the same anesthetic agents without verapamil. In this group, ICP and CPP were unchanged. The authors conclude that calcium entry-blockers, such as verapamil, should be avoided in patients with compromised intracranial compliance unless ICP is being monitored and proper therapy for intracranial hypertension can be rapidly instituted.