An inbred strain has been developed which exhibits some characteristics of aging in mice as young 6 months of age. The strain was designated "Senescence Accelerated Mouse" (SAM). A subline of the SAM strain, P/8, has an early onset of impaired learning in appetitive and aversive training tasks. Simple aversive and appetitive tasks were learned normally up to 12 months of age, whereas more difficult tasks detected impairment as early as 6 months of age while the mice still had good general health. Comparable impairment of learning and memory in C57BL/6Nnia mice was not detected until about 24 months of age which is near the end of the strain's lifespan when general health declines. In the present study, we report age-dependent impairment of acquisition and retention for footshock avoidance conditioning. Long-term (1 week) but not short-term (1 h) retention was adversely effected by aging. In 12-month-old P/8 mice, practicing the avoidance response (overtraining) did not alleviate the impairment of long-term memory processing.