The effects of thialbarbital, diethyl ether, and propanidid on the midbrain reticular formation and the cerebral cortex were studied in the cat. Thialbarbital caused marked depression of the activity of the reticular formation and only slight depression of cortical activity. Inhalation of ether caused early depression of synaptic input to the reticular formation without significantly influencing the functional state of the reticular formation itself. In the cortex ether caused early and marked depression. Propanidid caused less inhibition of the reticular formation than did thialbarbital. The significance of the enhancement of cortical responses in the mechanism of the production of general anesthesia by propanidid is not yet clear. The data suggest that there is no universal mechanism of general anesthesia which can explain the effects of different general anesthetics on various structures of the central nervous system.