Despite ready induction of severe limbic status epilepticus by systemic kainic acid (KA) in infant rats, excitotoxic neuronal injury has not been observed. The mechanisms of this resistance of the immature hippocampus to excitotoxicity are unknown. Acid fuchsin stain has been used as a marker of irreversibly injured neurons in the adult brain. We speculated that the dye might map reversibly injured neurons in the infant. Subsequent to KA-induced status epilepticus in 11-day-old rats, acid fuchsin stain was evident in the hippocampal CA3, CA1, dentate gyrus and hilus by 24 h, peaked at 48 h and disappeared by 6 days, without evidence for neuronal loss. Acid fuchsin may be a useful tool for delineating the distribution of reversibly injured immature neurons in experimental seizure paradigms.