Gout and urie acid lithiasis are known to have affected mankind for thousands of years. It is only recently, however, that great progress has been made in the understanding of the processes involved in purine metabolism and its disorders in man. The key enzymes active in the various pathways of purine synthesis and degradation have become known and their properties are the subject of intensive study. Major contributions to the knowledge of normal purine metabolism in man have derived from the study of inborn errors in patients with purine disorders, specifically complete and partial hypoxanthine-guanine phosphoribosyltransferase deficiency. Mutations of other enzymes involved in purine metabolism are