Rats display an age-related impairment in learning and memory; however, few studies have systematically examined this relationship in multiple strains. The present study used a repeated acquisition water maze task to test the hypothesis that age-related decreases in learning and memory occur at different rates in three strains of rats, i.e. Sprague-Dawley (SD), spontaneously hypertensive (SHR), and Wistar Kyoto (WKY) rats. All three strains of rats displayed age-related decreases in spatial learning and memory; however, the rate of decline differed between the strains. Compared to young rats of the same strain, only SHR were significantly impaired at 12 months of age. All three strains displayed moderate impairment in learning the task at 18 months of age, and at 24 months of age all three strains of rats were severely impaired in the task, but SD performed best at 18 and 24 months of age. Further, SD and SHR displayed a probe trial bias at 3 months of age, but only SD had a bias at 12 months of age and none of the rats showed the bias at later ages. Thus, in these three strains, age-related impairment of spatial memory proceeds at different rates. Copyright (C) 2000 Elsevier Science Inc.