The effect of cryopreservation on the cytotoxic activity of lymphokine-activated killer (LAK) cells was studied. LAK cells were generated by incubating peripheral blood lymphocytes for 3-5 days with recombinant interleukin-2 (rIL-2) and then cryopreserved using a programmed freezer. Cytotoxicity was determined in a 51Cr release assay. After thawing, the LAK cells had reduced cytotoxicity (25.5-39.1% as compared to the original lytic units). Cytotoxic activity could be restored to pre-cryopreserved levels by reincubation with rIL-2 for 2 days after thawing. Thus, maximal cytotoxicity of cryopreserved LAK cells could be achieved by incubation with rIL-2 before and after the freezing process. The level of cytotoxicity was comparable to that of LAK cells from fresh peripheral blood lymphocytes. Cryopreserved LAK cells may have potential in adoptive immunotherapy.