Dimerization equilibria and dismutation kinetics of fluorenone and xanthone ketyl radicals were studied by electrochemical methods at various pH. The dimerization equilibrium constant in aqueous-ethanolic solution is 7.1×1011 and 1.3×1013 M–1 for neutral fluorenone ketyl, and for neutral xanthone ketyl, respectively. Dimerization constants for the RH (neutral radical)+R–(radical anion) systems are much lower; those for R–+R– are negligible. Dismutation kinetics were resolved into component reactions. Rate constants of dismutation RH+R– are much higher than those found for RH+RH or R–+R– reactions. The kinetics support the electron-transfer mechanism of dismutation of ketyls.