The nature of azolignin chromophoric groups was studied by alternating-current polarography, integral and differential spectrophotometry methods. It was shown that spectral properties of lignin azoderivatives were determined by the presence of equilibrium forms of azo- and quinone-hydrazonic groups. The molecular extinction coefficients and equilibrium constants of azo- and quinone-hydrazonic forms and share of each of tautomeric forms in total (integral) extinction at vatious pH were determined. It was shown that both of tautomeric forms are distinct only on the differential absorption spectra of azolignin; on the integral spectra, the distinct absorption maxima are absent.