In previous studies using male rodents, context change disrupted a fear response at a short, but not a long, retention interval. Here, we examined the effects of context changes on fear responses as a function of time in male and female rats. Males displayed context discrimination at all intervals, whereas females exhibited generalization by 5 d. Ovariectomized females with no hormone replacement displayed context discrimination at 5 d, whereas those receiving 17ß-estradiol generalized their fear response to a neutral context. These results demonstrate that fear generalization for contextual cues occurs faster in female rats and is mediated, in part, by estrogens.