The aim of this study was to investigate the brain cortex Na(+)-K+ ATPase activity in rats made diabetic by streptozotocin and epileptic by pentylenetetrazol. Streptozotocin diabetic rats showed a significant decrease in brain cortex Na(+)-K+ ATPase activity whereas the pentylenetetrazol treatment caused no significant change in enzyme activity. On the other hand, no brain cortex Na(+)-K+ ATPase activity could be detected in all the diabetic rats treated with pentylenetetrazol. Our results concluded that reduced Na(+)-K+ ATPase activity in streptozotocin diabetic rats may contribute to the pathogenesis of metabolic complications of the central nervous system, and that the undetectable enzyme activity in diabetic convulsing rats may result from considerable damage or necrosis of brain tissue during pentylenetetrazol seizures.