The Tetramer technology is a new process which allows the direct and automated quantification of Tcells. By means of soluble MHC molecules in form of Tetramers as fluorescent probes, antigen specific T-cells are marked solidly and can be detected automatically. The fluorescent probes are already used for monitoring of T-cell reactions against CMV (during transplantations and stem cell transfer), HIV, Hepatitis-B and C and for analysis of tumor-specific T-cells.