Guanidinosuccinic acid (GSA) is a guanidino compound found in mammalian central nervous system and physiological fluids. Its level has been found to be greatly increased in serum and cerebrospinal fluid of patients with renal failure, and the compound is suggested to play a role in uremic encephalopathy. In this report we examined the behavioral, electrographic and morphological effects of intrahippocampal GSA injection in unanesthetized rats. Intrahippocampal administration of 2 microliters GSA solution (3.5 nM) was followed by behavior observation, and electrohippocampographic and electrocorticographic recording. GSA-injected animals showed partial clonic seizures leading to generalized clonic seizures, and eventually status epilepticus. These were accompanied by epileptiform electrographic discharges. During generalized clonic seizures, the electrohippocampogram showed arythmic bursting spikes. Epileptiform electric activity persisted even after the generalized clonic convulsions had stopped, and lasted until the animals were killed, 5 days following injection. Microscopic examination of brain slices of these rats revealed severe neural damage in CA1 area of hippocampus. Treatment of rats with the non-competitive NMDA receptor antagonist ketamine prevented both partial and generalized clonic seizures, epileptiform electrographic discharges, and GSA-induced hippocampal damage.