DHE, LSD, mescaline, ergotoxine and dibenamine were examined for effects on respiration and formation of lactic acid by preparations of guinea pig cerebral cortex in glucose-saline media. These processes in normal tissue were not very sensitive to the added agents, but on stimulation by electrical impulses became much more sensitive, inhibition being observed with mescaline at 10-3M and with the ergot derivatives and dibenazmine at 10-5M. In several cases these concentrations were 1/30 of those which affected metabolism in the absence of electrical stimulation. Within the range of concentrations in which they were effective, the agents inhibited respiration and glycolysis to similar degrees. The effect of DHE was not affected by the presence of adrenaline nor that of LSD by the presence of hydroxytryptamine (serotonin).