The pteridines in their multitude of forms fulfill many roles in nature ranging from pigments to cofactors for numerous redox and one-carbon transfer reactions. This extraordinary diversity of function is unified by the unique chemistry of the pteridine heterocycle. The International Symposium on the Chemistry and Biology of Pteridines and Folates is a forum for presenting recent and exciting advances in this expanding field. In of ideas results that has often stimulated bringing together various disciplines, a synergy fresh approaches to major problems. The Tenth International Symposium held at Orange Beach, Alabama, March 21-23, 1993, proved no exception by providing new insights into folate enzymology, tetrahydrobiopterin and molybdopterin biosynthesis and function, enzyme synthesis and regulation, along with novel synthetic strategies for producing compounds that will expedite further study. The many outstanding scientific contributions found in the following chapters, which represent the work presented at the Symposium, are a reflection of the significant advances made since the Ninth International Symposium held in Zurich in 1989. Since the 7th International Symposium in St. Andrews, Scotland, a tradition has evolved of honoring scientists who have made outstanding contributions to pteridine research with a Gowland Hopkins medal and lectureship. Sir Frederick Gowland Hopkins initiated the first investigation of what later proved to be pteridines in his studies of the yellow and white colors of butterflies.