The effect of a variety of substituents on the polarographic behaviour and acid-base equi- libriUm (revealed spectrophotometrically) of 2-[N-(phenyl) - acetomidoyl ]-l,3-indandione has been studied in wide pH range buffer Solutions (pH~ 3-12). The application of the linear free energy relationships using E^ values with different s sets showed a weak dependence while pKa- a sets showed a good correlation