Cytomegalovirus (CMV) infection remains a significant problem in allogeneic stem cell transplant (SCT) recipients despite the availability of effective antiviral drugs. This problem concerns patients which are unable to mount an effective T-lymphocyte response against CMV. Therefore, the development and use of tetramer technology to enumerate CMV-specific T cells will be valuable to identify these patients as early as possible. Here, we review clinical studies in which CMV-specific CD8(+) T cells have been monitored in allogeneic SCT recipients using tetramers in the context of similar studies that are based on functional assays of CMV-specific T cells. The results thus far warrant the further development of tetramer technology as a diagnostic tool to monitor CMV-specific T cells in SCT recipients and other groups of immunocompromised patients threatened by CMV.