The rate of synthesis of GABA, the major inhibitory neurotransmitter, was determined in parietal cortex and hippocampus during SE induced by systemic administration of lithium (3 mEq/kg) followed 20 h later by pilocarpine (100 mg/kg) in 1-4-week-old rats. Our results show that the immature hippocampus is better capable of maintaining GABA synthesis in the face of SE at the earliest stages of development studied (74.1% of basal in 1-week-old) and that development results in a progressive decline in the ability to maintain GABA synthesis in the face of SE (44.1% of basal by 4 weeks) that may parallel the ontogeny of self-sustaining seizures. Our data describe an aspect of developmental GABA neurochemistry which may in part explain the relative resistance of the immature hippocampus to seizure spread and of certain types of seizure-induced damage.