(1) Tautomeric transformations may take place in these hydroxyazo-compounds. (2) We may assign A (azo)-form to the neutral solution and R (red)-form to the alkaline. (3) In general, one band can be shown in the absorption curves, except when the hydroxyl-group takes an ortho-position with regard to the azo-group. (4) Hydroxyl- and nitro-radicals in para-position with respect to the azo-group are most effective in the absorption curve. (5) The methyl-group has generally a hyperchromic influence upon the non-methylated compounds.