It is often stated in the literature that vitamin C megadoses induce systemic conditioning that can lead to "rebound scurvy" when supplementation is discontinued. Gerster and Moser have critically reviewed the evidence for this effect. There appear to be only three reported cases of rebound scurvy in adults, and the reviewers conclude that these reports are "anecdotal and not well founded." No blood vitamin C levels were determined in any of these cases. One patient developed symptoms less than two weeks after discontinuing vitamin C supplements; since body vitamin C stores cannot be depleted this quickly, it is very doubtful that this case was true scurvy. In the other two cases, no information about the patients' dietary habits was collected. It is noteworthy that no cases of rebound scurvy have been reported in clinical trials of vitamin C megadoses. Concern that infantile scurvy can be induced in utero if a pregnant woman takes vitamin C megadoses is based on the only published report--one that is "poorly documented and not convincing." Only two cases were involved; in both instances the infants apparently received 60 mg of vitamin C daily, and the mothers had taken only about 400 mg of vitamin C daily during pregnancy (not an unusually high dose). The cases occurred in a region in Canada in which infantile scurvy is relatively frequent and thus may have been unrelated to the mothers' vitamin C intakes. The proposed mechanism of action of rebound scurvy is that constant high vitamin C doses condition the body, through enzyme induction, to discard the vitamin at an increased rate, and that this mechanism continues to operate when vitamin C supplementation is stopped. Attempts to demonstrate this effect in guinea pigs and humans have produced "highly contradictory results." Rebound scurvy has never been induced experimentally in either species, and the metabolic effects of discontinuing vitamin C supplementation have varied and have been interpreted in diverse ways. In guinea pigs, adverse effects have been seen only in studies in which near-toxic vitamin C doses or unphysiological methods of vitamin C administration were used. The reviewers conclude that "the claim of a conditioning effect of high vitamin C doses appears to be unfounded."