The effect of sufentanil on human cerebral blood flow (CBF) was studied in seven unpremedicated, healthy volunteers 31 ± 3.5 yr of age (mean ± SD) and either sex. CBF (ml · 100 g−1· min−1) was measured noninvasively with the133Xe clearance technique and a scintillation camera before and after sufentanil 0.5 μg/kg administered intravenously. This technique provides values for global blood flow and for gray and white matter blood flow, and from 13 preselected regions in one hemisphere. After the administration of sufentanil, the volunteers were stimulated verbally in order to prevent their loss of consciousness and hypercarbia. Heart rate (HR), arterial pressure, oxyhemoglobin saturation, and end-tidal CO2(ETCO2were recorded during the measurements. Neither global CBF (46.1 ±1.6 control and 43 ± 1.9 after sufentanil, mean ± SEM) nor gray (76.5 ± 3.2 and 70.9 ± 6.1) or white (22.7 ± 1.5 and 24.2 ± 1.6) matter blood flow changed significantly after sufentanil administration. As well, no significant differences in HR (72 ± 4 control and 79 ± 4 beats per min after sufentanil) and ETCO2(39.8 ± 1.4 and 41.1 ± 1.1 mmHg) were observed. It is concluded that sufentanil has no significant effect on CBF in healthy human volunteers.