These volumes contain the papers which were presented at the Third International Symposium on Purine Metabolism in Man held in Madrid (Spain) in June, 1979. The previous meetings in the series were held in Tel Aviv (Israel) and in Baden (Austria) in 1973 and 1976, respectively. The proceedings were also published by Plenum. Knowledge of the pathophysiology of the purines has developed greatly since the 1950's when it was mainly related to clinical gout, and it is now relevant to many fields of Medicine and Biology. These volumes include papers reporting new work on clinical gout and urolithiasis as well as on some of the subjects which have featured prominently in the previous volumes, including: regulatory aspects of the intermediary metabolism of purines and related compounds, enzymology, methodology, and the results of mutations which affect purine metabolism. However, there have been many new developments during the last three years and the scope of the communications reflects not only increasing depth of knowledge, but also a widening of the field. This publication has clinical and fundamental implications for internal medicine, pediatrics, urology, biochemistry, immunology, genetics, and oncology. It is interesting to compare the scope of this volume with that of its predecessors. The main emphasis has shifted from the study of gout and the dissection of metabolic pathways to encompass investigations in the fields of oncology, immunology, and lymphocyte physiology. There are pointers to possible implications in relation to cardiology and neuromuscular diseases, which may well prove to be growing points for the future. In spite of considerable work on the mechanism of urinary stone formation, the inter-relationship between uric acid and calcium oxalate urolithiasis remains obscure. It is no longer logical to discuss clinically related purine research without including comparable work in the less studied field of pyrimidine metabolism. Some such studies were reported at the Madrid meeting, and this development will be formally encouraged in the future. The use of some animal and single cell models as tools with complexity intermediate between man and the single or multi-enzyme systems represents another new development in this area of clinical investigation.