In two experiments, ovariectomized rats were given a novel diet prior to the implantation of a fused pellet of estradiol (E2 pellet). In short-term (3 weeks) ovariectomized rats, the suppression of food intake induced by estrogen was not affected by the introduction of the novel diet. However, a sensitive two-choice preference test revealed that subjects implanted with the E2 pellet had a lesser preference for the novel diet than controls implanted with the vehicle pellet. In long-term (18 weeks) ovariectomized rats, implantation of the E2 pellet had a large effect on the consumption of the novel diet. Intake was reduced to less than 1 g in all subjects on Days 3-7 after E2 pellet implantation. A subsequent two-choice preference test indicated the presence of a strong aversion to the novel diet in the estradiol-treated rats relative to the controls. These experiments show that estradiol can induce conditioned taste aversions that have either no effect on intake or totally suppress food intake, depending upon postovariectomy time.