By means of the hypovolemic oligemia model, an experimental blood flow disturbance was simulated in the cat brain. It could be shown in N2O/O2-anesthetized animals, that a 30–40% reduction in cerebral blood flow, caused by an oligemia-induced drop in blood pressure (mean arterial blood pressure: 45 mm Hg), led to an instability in cerebral electrical activity. In the course of the 2-hour period of oligemia the EEG activity decreased below the normal energy values by about 30–50%. We investigated in this model whether the vasoactive substance papaverine or the neurochemically active drug dihydroergotoxine mesylate (DHET; active substance of Hydergine®) is able to influence these cerebral blood flow disturbances, which are manifested as a depression of EEG activity. Our experiments have shown that DHET exerts a protective effect on the oligemically disturbed brain metabolism (stabilization of EEG activity and shift of pO2 distribution in direction of normotonic state). This protective action may be related to its regulating effect on CNS catecholamines, since other substances with protective actions (barbiturates, dopamine, phenoxybenzamine, etc.) also influence catecholamine metabolism. Papaverine, on the other hand, shows a marked vasoactive effect without preventing the breakdown of the EEG activity. In spite of increasing local cerebral blood flow, papaverine has no positive effect on the oligemia-induced decline in cerebral pO2 values. Therefore it can be concluded from our oligemia experiments that this substance does not improve nutritional blood flow, but rather leads to a shunt perfusion.