A new modification of an HLA-DR typing technique is described which makes DR typing as rapid and simple as routine HLA-A,B,C typing. In this new method, designated the TM1 technique, carboxyfluoresceindiacetate labeled peripheral blood lymphocytes are added directly to DR typing trays. The T cells are then lysed by addition of TM1, a pan-T cytotoxic IgM monoclonal antibody, and residual B-cell reactivity with cytotoxic DR alloantibodies is read as in routine fluorochromasia microlymphocytotoxicity. HLA-DR typing by the TM1 technique compares favorably to typing by methods using B cells enriched by sheep red blood cell rosetting or by Degalan bead columns. The TM1 technique also works well with cells that have been cryopreserved as well as with cells that have been separated from whole blood drawn as much as 3 days earlier. Finally, because TM1 is so effective in lysing normal T lymphocytes, this antibody may prove useful in functional in vitro and in vivo studies requiring T-cell depletion.