- A yellowish-white, crystalline purine base, C<sub>5</sub>H<sub>4</sub>N<sub>4</sub>O<sub>2</sub>, that is a precursor of uric acid and is found in blood, urine, muscle tissue, and certain plants.
- Any of several derivatives of this compound.
- A type of purine obtainable as a white microcrystalline powder, C5H4O2N4, present in muscle tissue, in the liver, spleen, pancreas, and other organs, and also in urine (in small quantities) and some urinary calculi, and in the juices of certain plants; -- so called because it leaves a yellow residue when evaporated to dryness with nitric acid. It is also present in guano. Xanthine is closely related to uric acid.
- Any of a group of <xref>alkaloids</xref>, that include <xref>caffeine</xref>, <xref>theophylline</xref>, and <xref>theobromine</xref> as well as the <xref>parent compound</xref>, a precursor of <xref>uric acid</xref> found in many organs of the body.
- crystalline oxidation product of the metabolism of nucleoproteins; precursor of uric acid; found in many organs and in urine