Analyses in non-aspirin takers finding salicylic acid (SA) and hydroxylated metabolites in serum also SA and salicyluric acid (SU) in urine led to a re-evaluation of dietary sources of salicylates. Fruit and vegetable sources explained higher levels found in drugfree vegetarians, which overlapped with those from patients on low dose aspirin. That drug's chemo-protective action in cancer is, at least partially, attributable to its principal metabolite, SA-which we believe contributes to the

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... its of a vegetarian diet. However, diet is unlikely to be the sole source of the circulating salicylate found in aspirin-free animals and man. We adduced evidence for its persistence in prolonged fasting and biosynthesis in vivo from labelled benzoic acid. We review the roles, defined and potential, of SA in the biosphere. Emphasis on the antiplatelet effect of aspirin in man has detracted from the likely pivotal role of SA in many potential areas of bioregulation-probably as important in animals as in plants. In this expanding field, some aspirin effects, mediated by apparently conserved receptors responding to SA, are discussed. The perspectives revealed may lead to re-evaluation of the place of salicylates in therapeutics and potentially improve formulations and drug delivery systems.