The mouse homolog of the Gibbon ape leukemia virus (GALV) receptor (Glvr-1) was mapped to mouse Chromosome 2 (Chr 2) by Southern blot analysis of somatic cell hybrids and positioned on this chromosome using an interspecies genetic cross. Mouse Chr 2 also encodes a receptor (Rec-2) for the wild mouse virus M813. To investigate whether Glvr-1 and Rec-2 could be the same gene, we sought evidence for sequence homology between the env- genes of their respective viruses. Southern blot hybridization with GALV-derived env and pol-env probes failed to detect any homology between GALV and M813, but did show that all mouse species tested carry numerous copies of GALV-related sequences. We speculate that a functional receptor for GALV-related viruses was expressed during Mus evolution.