The determination of pyridoxal in the presence of pyridoxal-5-phosphate may be1 based on the difference between the total wave-height obtained at pH about 9, where both substances give a diffusion-controlled wave and that obtained in acid media, where pyridoxal alone shows a kinetic current2. The mixture of pyridoxal and pyridoxal-5-phosphate alternatively can be converted to oximes and their four-electron waves at pH 8,5 can be resolved using derivative curves1.