AbstractBiochemical information about the ubiquitous pteridines has become generally available only within the last fifteen years. This delay can be traced to the chemical lability of these compounds and their small concentrations in organisms. New methods of isolation and isotopic techniques have provided data on the biosynthesis, anabolism, and catabolism of this class of compounds. Hydrogenated pteridines are recognized today as cofactors for various mixed function oxygenases and are involved in cellular electron transport. Further unknown catalytic functions for pteridines in cellular metabolism are indicated by their physiological activity, negative redox potentials, and histoautoradiographic data.