Two isozymes of glucosephosphate isomerase (GPI:E.C. 5.3.1.9.) were observed in the mosquito Aedes togoi by means of agar gel electrophoresis. The locus (Gpi-1) controlling the more anodally migrated isozyme (GPI-1) was located on linkage group 1 (sex chromosome) of this species; the gene arrangement being Gpi-1--(18.2 map units)--To-2 (tetrazolium oxidase-2)--(27.3 map units)--M/m(sex)--(about 40 map units, as estimated by previous studies)--s (straw-colored larva). Linkage homologies concerning Gpi and Odh (octanol dehydrogenase) are compared among three species: Ae. aegypti, the Ae. scutellaris group, and the Ae. triseriatus group in terms of chromosomal evolution.