Many findings suggest that changes in circulating estrogen levels influence cognition, in some cases impairing performance and in others enhancing performance. One interpretation of these mixed effects is that estrogen biases the strategy used to solve a task. To test this idea, young adult female rats, ovariectomized for 21 days, were trained after acute hormone or control treatment in 2 very similar tasks with different cognitive requirements. One task required place learning and the other response learning. Rats given two 10-microg injections of estradiol 48 and 24 hr before training learned the place task significantly faster than did rats without estradiol. Conversely, rats without estradiol performed better on the response task than did rats with replacement. These data suggest that the cognitive actions of estrogen may be task-specific by modulating the relative contribution of different learning and memory systems.