Intracranial pressure measurements were made during nitroglycerin-induced hypotension in the cat anesthetized with halothane. A total of 48 individual observations were made in eight animals. The administration of sufficient nitroglycerin to decrease mean arterial pressure from a control value of 87 ± 7 torr by 12 ± 4 torr resulted in an increase in mean intracranial pressure from a control value of 7 ± 2 torr to 12 ± 2 torr. Larger decreases in mean blood pressure were associated with larger increases in intracranial pressure. The increase in intracranial pressure was similar to that previously reported for nitroprusside, and greater as well as more reproducible than that reported for trimethaphan. Thus, nitroglycerin may produce significant increases in intracranial pressure, and this may be a limiting factor in its clinical use.