The human endogenous retrovirus ERV3 possesses an open reading frame for a truncated envelope, which is expressed as mRNA and protein. Here we examine the env sequence in primates for evidence of evolutionary conservation. ERV3 sequences were amplified by PCR from genomic DNA of great ape and Old World primates but not from New World primates or gorilla, suggesting an integration event more than 30 million years ago with a subsequent loss in one species. In the chimpanzee, the protein sequence of Env is 98.18% identical to that of human. In other species the identity falls (93.71% in rhesus macaque) in proportion to the separation from the human lineage. Start and stop codons and domains of functional significance in the envelope protein are conserved. The evolutionary conservation of the ERV3 envelope suggests a beneficial function, though the loss from gorilla shows that it is not essential for survival or reproduction.