TCD50 values for thermally resistant tumors have been significantly reduced. The therapeutic ratio has been improved for some tumor-normal tissue situations and treatment protocols, but not for others. The oxygen enhancement ratio (OER) for hyperthermic damage may be congruent to 1; if this is true for tumor cells in vivo, the combination of hyperthermia and radiation should improve the therapeutic ratio to the extent that hypoxic cells are critical. There does not appear to be a differential response to hyperthermia by the normal foot or tumor growing in the foot pad for the following two parameters: (a) relationship between heating time to produce the specified response and the level of heating, and (b) effect of fractionation of hyperthermia.