Cytotoxic T cell recognition of virus-infected cells requires the presentation of viral peptides by class I HLA molecules on the cell surface. We report here that cytomegalovirus (CMV) infection of human fibroblasts results in a progressive decrease in the cell surface expression of class I HLA and beta 2-microglobulin (beta 2m) such that in the late stages of infection the majority of infected cells have no detectable surface class I HLA. Coincident with decreased surface expression of class I HLA was an increase in his cytoplasmic expression. Confocal scanning laser microscopic analysis demonstrated that class I HLA and beta 2m accumulate in a perinuclear compartment inside the CMV-infected cell. Our data thus support the concept that CMV infection induces altered transport of class I HLA to the cell surface. We suggest that the virus has evolved this mechanism as a strategy to avoid T cell recognition of infected cells.