Seizures were induced in 7-day-old rats by intraperitoneal injection of DL-homocysteine thiolactone. Phosphocreatine (PCr), ATP, glucose, glycogen and lactate were determined in the cerebral cortex during various intervals after injection, corresponding to the early, as well as long periods of seizure activity. The unchanged levels of ATP, a very mild PCr decline and a pronounced accumulation of lactate (in the face of modest changes in brain glucose and glycogen) were observed. These results suggest that the immature rat brain is able to compensate energy expenditure associated with seizure activity by increased energy production, mainly due to increased anaerobic glycolysis. It remains to be determined whether a similar conclusion is also valid for other brain regions, e.g. subcortical structures.