Cytotoxic lymphocytes (CTL) can be generated in mixed lymphocyte culture and cryopreserved after a 6-day sensitization phase. CTL tested after storage in liquid nitrogen do not show lysis of autologous target cells and can mediate strong cytotoxicity against other target cells. This lysis shows the same specificity as that of the corresponding fresh CTL. The ability to cryopreserve CTL enables performance of sequential CML testing. Data from separate CML experiments can be pooled using a percent relative cytotoxic response (%RCR) to normalize values within individual experiments. Together, these methods provide a standardized cell-mediated lympholysis technique.