We determined the complete nucleotide sequence of baboon endogenous virus (BaEV) strain M7. The total length of the retroviral DNA is 8, 507 base pairs. The order of viral proteins encoded is NH₂-p12-p15-p30-p10-COON in the gag, NH₂-protease-reverse transcriptase-endonuclease-COOH in the pol, and NH₂-gp70-p20E-COON in the env genes. The transmembrane env protein, p20E, contains an amino acid sequence closely related to the "immunosuppressive peptide." Uncharacteristically, the pot and env genes do not overlap and are translated in the same frame. The deduced amino acid sequence of BaEV is related to 1) reticuloendotheliosis virus strain A in both the pol and env regions, 2) murine leukemia viruses in the pol but not in the env region, 3) simian type D retroviruses in the env but not in the pol region. This suggests that env genes in retroviruses may have been independently interchanged during evolution.