Abstract 17β-Estradiol (E 2) can serve as a potent unconditioned stimulus in producing a conditioned taste aversion to saccharin in rats, with the effect being greater in males than in females. To determine whether the female's lower susceptibility to such conditioning is due, in part, to early experience with estrogen, we performed the following experiment. First, we pretreated groups of prepubertally ovariectomized female rats with either sesame oil (control group) or low doses of E 2 (0.3, 0.75, or 1.50 μg). Second, in subsequent conditioning sessions, we presented a 0.2% saccharin solution to the rats prior to the injection of 100 μg of E 2 (the unconditioned stimulus). Third, we tested the magnitude of the conditioned aversion to the saccharin solution and its tendency to extinguish during the following week. The E 2-pretreated animals evidenced significantly weaker taste aversions and extinguished them more rapidly than did the oil-pretreated controls, even at the lowest E 2 pretreatment dose, suggesting that prior experience with low levels of estrogen can significantly mitigate, in female rats, the magnitude of a conditioned taste aversion produced by a high dose of estrogen.