Trichoxanthin is a granular yellow pigment occurring in hair matrix and hair medulla of yellow and red guinea pig skin. It is insoluble in organic and dilute mineral acids, water and organic solvents, irregularly soluble in dilute alkali and promptly removed by methylation though not by acidified higher aliphatic alcohols. It reduces ferric ferricyanide and ammoniacal silver promptly, acid silver nitrate slowly. Indole reactions, azo-coupling reactions and Gibbs's phenol reaction are negative. It is strongly basophil at pH 1 and binds ferrous ions, in these characters resembling melanin. It is more promptly bleached by HNO3, CrO3, KMnO4 and CH3CO3H than is cutaneous melanin of the same species and its reduction reactions are more rapidly affected by oxidants. Reduction of acid silver nitrate is not appreciably accelerated by prior hydrosulfite reduction, in distinction from melanin. On the basis of the modifications of the metal reduction reactions by oxidants and reductants, the possibility of a p-quinhydrone structure is suggested.