Xanthine (/ˈzænθiːn/ or /ˈzænθaɪn/, from Ancient Greek ξανθός xanthós "yellow" due to its yellowish-white appearance; archaically xanthic acid; systematic name 3,7-dihydropurine-2,6-dione) is a purine base found in most human body tissues and fluids, as well as in other organisms.