Conducted 4 experiments with Swiss-Webster mice (N = 488) to examine the development of memory of an escape response between 3-11 days of age. Ss were given 25 training trials in a straight-alley escape task and then retested at various retention intervals. Results show that 5- and 7-day-old Ss had a retention capacity of less than 6 hr. At 9 days of age, however, retention capacity greatly increased to at least 96 hr., suggesting that a period of maturational development critical to long-term memory processes occurs at 9 days of age in the neonatal mouse. (15 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)