The membrane impedance change of optically active membranes due to interactions between amino acids and the membrane was also employed to discriminate D-amino acids from L-amino acids successfully [G-8]. From these results for D- and L-amino acids, it was suggested that a sufficient effect occurs in tlie membrane characteristics that the occurrence of an appropriate reaction such as diastereomer formation results in the membrane potential and impedance changes depending on the chirality of the amino acid.