The in vitro radiobiologic survival values (.hivin.n [extrapolation number] > D0 [effective radiation dose] of 4 tumor lines derived from human hematopoietic tumors were studied. These cell lines were HL60 (.hivin.n = 1.3, D0 = 117 rad [1.17 Gy [Gray]]), promyelocytic leukemia; K562 (.hivin.n = 1.4, D0 = 165 rad [1.65 Gy]), erythroleukemia; 45 (.hivin.n = 1.1, D0 = 147 rad [1.47 Gy]), acute lymphocytic leukemia; and 176 (.hivin.n = 4.0, D0 = 76 rad [0.76 Gy]), acute monomyelogenous leukemia. More cell lines must be examined before the exact relationship between in vitro radiosensitivity and clinical radiocurability is firmly established.