OBJECTIVE: Some research has shown that learning and memory function impairments in rats with hypothyroidism are associated with triiodothyronine (T3) deficiency in neurons. This study aimed to investigate the effects of L-T3 administration on learning and memory behaviors in neonatal mice with excitotoxic brain damage. METHODS: Seventy-one 5-day-old ICR neonatal mice were randomly assigned to five groups: controls that received intracerebral and intraperitoneal injections of phosphate buffered saline (PBS) (n=14); a group that received intracerebral injections of ibotenic acid (IA) and intraperitoneal injection of PBS (n=14); 3 groups that received intracerebral injections of IA and intraperitoneal injection of L-T3 at 0.2, 0.5, and 1 μg/kg, respectively (n=14-15). Intraperitoneal injections were done 1, 24, 48, 72 and 96 hrs after intracerebral injections. Learning and memory functions were evaluated by the Y-maze discrimination learning test on postnatal days 33-34. RESULTS: The learning and memory functions in the highest L-T3 dose group were significantly better than those in the IA, and the lower L-T3 dose groups, presenting with decreased number of trials to criterion ［15.8±4.5 vs 21.3±6.3 (IA group), 20.5±6.0 (0.2 μg/kg L-T3 group) or 21.0±6.5 (0.5 μg/kg L-T3 group); P<0.05］, and achieving a higher correct percentage ［91.4±9.5% vs 79.3±10.0% (IA group), 77.9±14.2% (0.2 μg/kg L-T3 group) or 80.7±12.2% (0.5μg/kg L-T3 group); P<0.05］. CONCLUSIONS: High-dose L-T3 (1 μg/kg) may improve learning and memory functions in mice following excitotoxic brain damage.［Chin J Contemp Pediatr, 2010, 12 (4):284-286］