Low-dose ketamine is recommended in patients requiring sufficient analgetic support in emergency situations. There is still controversy in the discussion on ketamine-induced effects on cerebral blood flow and intracranial pressure. We investigated the effect of 0.25 mg x kg-1 ketamine i.v. on the blood flow velocity in the basal cerebral arteries in 10 healthy volunteers by transcranial Doppler sonography (TCD). Peak and mean blood flow velocities, pulsatility index, arterial blood pressure, heart rate, oxygen saturation and end tidal carbon dioxide tension were measured during the study. There was a significant increase in the hemodynamic parameters and in blood flow velocities, paralleled by a decrease in pulsatility index and constant values for oxygen saturation and CO2-tensions following injection of ketamine. The results indicate a transient stimulation of the cardiocirculatory system with a concomitant reduction of the cerebral vascular resistance. The question of informative detection of intracranial hemodynamics following application of intravenous anesthetics will be discussed.