Although 2,4,5-trihydroxyphenethylamine and 2,4,5-trihydroxyphenylalanine can give melanins on autoxidation, the yields are low, and spectroscopic experiments suggest that these compounds are not important intermediates in the formation of dopamine- and dopa-melanins, respectively. Autoxidation of 5,5′,6,6′-tetrahydroxybiphenyl-3,3′-ylenedi(ethylaminie), 5,5′,6,6′-tetrahydroxybiphenyl-2,2′-ylenedi(ethylamine), 5,5′,6,6′-tetrahydroxybiphenyl-2,3′-ylenedi(ethylamine), 2,3-bis-(3,4-dihydroxyphenyl)butane-1,4-diamine, and 5,5′,6,6′-tetrahydroxybiphenyl-3,3′-ylenedialanine also yields melanins. Polyphenol oxidase appeared to be less effective in catalysing oxidation of the first of these compounds than of dopamine; and almost ineffective in the cases of the 2,2′-, and 2,3′-isomers of the first.