The effect of high-frequency ventilation (HFV) on cerebral blood flow (CBF) at normal and elevated intracranial pressure (ICP) was compared with flows measured under the same conditions during intermittent positive pressure ventilation (IPPV). Renal, lung (bronchial artery supply), and cardiac blood flows also were measured during HFV and compared with flows observed during IPPV. Measurements were made in canines with stable hemodynamic variables and arterial CO2and O2tensions in the normal range. CBF during HFV was comparable to the CBF during IPPV. Following an increase in ICP to a mean of 44 ± 18 mmHg (SD), mean CBF decreased to 22.5 ± 11 ml · 100 g-1· min-1(SD) during IPPV and 21.7 ± 13.2 ml · 100 g-1· min-1(SD) during HFV. No statistical differences could be noted in regional or global flow as a function of ventilatory mode. Renal, lung (bronchial artery supply), and cardiac blood flows also showed no statistical variation between HFV and IPPV. Ventilator-synchronous fluctuations in ICP observed during IPPV were reduced during HFV at normal ICP and eliminated by HFV at elevated ICP.