Prior evaluations are frequently challenged and need to be revised. We propose that an important determinant of such revisions is the degree to which the challenge provides an opportunity to compare the target against a competitor. Whenever a challenge offers an opportunity, the information contained in the challene will carry a disproportionate weight in the revised judgments. We call this proposition the comparison-revision hypothesis. In Experiments 1 to 3, we manipulated comparison opportunity by varying the format of the challenge and examined the weights assigned to different inputs in the revised judgments. The results indicate that prior information about the target receives a greater weight under a noncomparative challenge (which provides information only about the target) than under a comparative challenge (which compares the target with a competitor). In contrast, information presented in the challenge receives a greater weight under a comparative challenge than under a noncomparative challenge. Interestingly, when presented in a comparative format, the information contained in the challenge received a relatively disproportionate weight even when the attributes presented in the challenge were less important than those on which the prior target evaluations were based. Results from Experiment 4 suggest that, under certain conditions, even a noncomparative challenge from a superior competitor can provide strong comparison opportunity and thus cause greater revisions in the prior evaluations of the target. Specifically, a greater elaboration of the initial target information and a high degree of commensurability between the target and competitor information jointly promote comparison opportunity and thus cause greater revisions of the prior target judgments. Our findings offer important extensions to previous research on the effects of amount and elaboration of prior target information on subsequent judgment revision.