The pathways of purine biosynthesis and degradation have been elucidated during the last 30 years; the regulation of the mechanisms involved is not yet fully understood, particularly with respect to quantitative aspects. Research into inborn errors of purine metabolism has provided valuable insights into purine synthesis and salvage pathways. Nutrition experiments using purine-free formula diets and supplements with defined purine sources permit precise descriptions of the influence of various dietary purines on uric acid formation. Supplements of dietary purines produce dose-proportional increases in plasma uric acid concentrations, uric acid pool size and renal uric acid excretion. The magnitude of these increases depends on the type of purine compound administered, which may limit the value of food tables for human dietetics. Purine content of food must be related not only to weight but also to energy and to protein, particularly if new foodstuffs or a vegetarian diet are ingested. Dietary purines appear to influence the biosynthesis of pyrimidines. In contrast to dietary purines, pyrimidines in the diet, if administered as nucleosides or nucleotides, are utilized in animals for the synthesis of nucleic acids. Much further work is necessary for a better understanding of the inter-relationships of purine and pyrimidine metabolism.