Cytomegalovirus (CMV) reactivation and disease remains an important clinical problem for patients after allogeneic stem cell transplantation. Impaired cellular immune control of viral replication is responsible for viral reactivation, and transfer of CMV-specific T cells from transplant donors can be effective in providing protection. Recent reports have indicated that the frequency of CMV-specific CD8+ T cells in the peripheral blood of healthy donors is surprisingly high. Here we demonstrate that by using a combination of human leucocyte antigen (HLA) Class I-peptide tetramers and magnetic selection it is possible to select CMV-specific T cells from CMV antibody-positive individuals to high purity. Reliable purification of CMV-specific T cells up to 99·8% of CD8+ cells was possible within hours, even when starting with a precursor frequency of < 0·1% of peripheral blood CD8+ T cells. CMV-specific T cells remained functional after the selection process. This novel form of antigen-specific T-cell selection should facilitate the selection of T cells for cellular immunotherapy to treat or prevent CMV disease after transplantation. In addition, this technique could potentially be applied to many antigens including against other infective agents and tumour-specific antigens.