Polyacrylamide slab gel electrophoresis disclosed clear discrimination among strains of the malaria vector-containing Anopheles leucosphyrus group of mosquitoes in East Asia. Nine strains of the group were studied at 7 protein loci and the strains could be distinguished into 5 taxa. No variation among strains was detected at Mdh and Pt-8. In the other 5 protein loci, Me, Odh, Lap-8, Lap-9, and Est-1, almost no overlapping alleles were found among all strains, which allowed the following distinction among the strains, confirming the designation made by Kanda et al. (1983, 1985): An. balabacensis dirus (THL), An. b. balabacensis A (KTD), An, b. balabacensis B (IMR), An. takasagoensis (TSG), and An, leucosphyrus (SWK). The former 4 taxa had been lumped into the An, balabacensis complex (Kanda et al. 1983, 1985), but there was no clear remoteness between the complex and An. Leucosphyrus at the protein level. The result was discussed in the light of recent developments in protein variation.