The Fifth International Symposium on Human Purine and Pyrimidine Metabolism was held in San Diego, California (U. S. A. ) in July and August of 1985. Previous meetings in this series were held in Tel Aviv (Israel), Baden (Austria), Madrid (Spain) and Maastricht (The Netherlands). The proceedings of each of these meetings were published by Plenum. The next meeting will be in Japan. This Symposium differed from those that went before in that it per­ mitted us to honor Dr. J. E. Seegmiller, Professor of Medicine at the University of California San Diego, for his many contributions to our understanding of purine metabolism in man. This publication is dedicated as a Festschrift to Jay. Dr. Richard W. E. Watts delivered the keynote address outlining in scholarly fashion the history of Dr. Seegmiller's accomplishments in research on purine metabolism and the great number of currently active scientists in this field who have worked with him. This address is published as the first contribution to Volume I. Dr. Dewitt Stetten, Jr. , was scheduled to be the speaker at our banquet. Unfortunate­ ly, he could not be with us. Dr. Seegmiller has written an appreciation of Dr. Stetten and his contributions to our field, and this has been pub­ lished following Dr. Watts' paper. The growth of knowledge in purine and pyrimidine metabolism continues to be exponential. The variety of subjects included in these volumes is impressive.