Lesions of CA 3 derived axons, comprising Schaffer's collaterals, were carried out in order to destroy their presumably glutamatergic nerve endings within CA 1. After a survival time of 20 days part of the stratum radiatum of CA 1 displayed statistically significant reduction of histochemically demonstrable glutamate dehydrogenase and succinate dehydrogenase activity by about 19 and 25 per cent, respectively, whereas alpha-glycerophosphate dehydrogenase was not affected. These findings are consistent with current biochemical and histochemical results on the relation between several glutamate producing enzymes and glutamatergic structures suggesting that glutamate dehydrogenase plays a major role in glutamate transmitter metabolism.