Summary The electrophoretic pattern of glucose-6-phosphate dehydrogenase (G6PD) was examined by microelectrophoresis in Polyacrylamide gel (PAG) in the presence in cathode buffer of nicotinamide adenine dinucleotide phosphate (NADP + ). Seven species of the genus Amoeba were investigated: A. proteus, A. lescherae, A. discoides, A. indica, A. amazonas, A. borokensis , and A. leningradensis (7 strains of A. proteus and one strain of each other species); 2 strains of Chaos carolinense and 1 strain of Poly chaos dubium were also studied. It has been found that in the 7 strains of Amoeba proteus of different origin (A, C, B, L, F, Bk and Da) the isozyme pattern of G6PD consists of 1–2 “slow” electrophoretic bands, located near the cathode, one band of intermediate mobility, and 1–2 “fast” bands, proximal to the anode (2 bands in strain B and one band in the 6 other strains). In strains A and C, the fast band may sometimes not be detected at all. The electrophoretic pattern of G6PD of A. lescherae does not differ from that of A. proteus (strain B), and the pattern of A. discoides is identical to those of the 6 other strains of A. proteus . Among 4 other Amoeba species, the fast band is detected but may sometimes be absent in A. amazonas and it is not found in A. indica, A. borokensis and A. leningradensis . In addition, two species, A. amazonas and A. leningradensis , show an additional band of intermediate mobility, absent in all the other species of Amoeba . The isozyme pattern of G6PD in Polychaos dubium is represented by only two minor bands of intermediate mobility. The two strains of Chaos carolinense , in contrast to all Amoeba species studied, do not show any G6PD electromorph proximal to the cathode, whereas fast G6PDs are represented by two bands in one strain and are absent in the other. It is concluded that there is a possibility of using isozyme patterns as additional taxonomic criterion in Amoebidae.