Primary infection with human cytomegalovirus (HCMV) is persistent and widespread, with symptoms that are mostly subclinical but can cause serious illness or death, particularly in immunosuppressed patients^1,2. Recently³, proteins from HCMV were shown to bind β₂-microglobulin (β₂-m) a protein that is normally found associated with the class-I major histocompatibility complex (MHC) antigens, which are essential for self-non-self recognition in the immune response⁴. These findings led to the proposal that the virus may use β₂-m binding as an infection mechanism⁵. Here we present evidence from DNA sequence analysis that HCMV encodes a molecule similar to the MHC class-I antigens of higher eucaryotes, and propose that this protein is responsible for the observed β₂-m binding. The deduced amino-acid sequence of the HCMV class-I-like protein reveals conservation of typical features of class-I structure, but we predict that the gene is not spliced, in contrast to the cellular genes.