To compare the long-term behavioral effects of chronic administration of excitatory amino acids in the mature and immature brain quisqualic acid (QA) and glutamate (GLU) were administered intraventricularly by osmotic pumps over 7 days in 20- and 60-day-old rats. Both age groups received identical dosages of QA or GLU. At age 90 days, all animals were assessed for abnormalities of learning and memory using the Morris water maze, emotionality using the handling test, and seizure threshold using flurothyl inhalation. No significant differences were found in either the water maze or handling test. However, 60-day-old rats receiving QA or GLU had more spontaneous seizures than the 20-day-old rats. In both age groups histological damage following QA and GLU was limited to the ipsilateral hippocampus, was maximum at the site of the catheter tube, and was similar in the two age groups studied. The adverse effects of long-term effects of chronic exposure to excitatory amino acids are similar in the immature and mature brain.