The hyperglycemia-induced in vivo metabolic changes pro4uced in subcutaneous murine RIF-1 tumors, grown on female C3H/Anf mice, were examined with 31P surface-coil NMR. Serum glucose levels were elevated 4-fold by bolus intrape& toneal injection of 0. Hyperglycemia, an increase in the serum glucose concentration ([Glc]b), has been reported to selectively enhance the thermal sensitivity of tumors and thereby represents a useful adjuvant of hyperthermia in the treatment of cancer ;1-5).The side effects associated with short-term hyperglycemia are minor (for nondiabetic subjects), the prominent effect being an increase in thirst, which can be relieved by increased intake of water (6). Although hyperglycemia alone had no effect on the growth rate in any of the tumors examined (5), hyperglycemia increased the thermal sensitivity of all rat and murine tumors examined (2, 4, 5, 10).Since the introduction of surface-coil NMR for studies of in vivo tissue (13) MATERIALS AND METHODSA radiation-induced fibrosarcoma, RIF-1, obtained from R. F. Kallman (Stanford University), was maintained by the serial in vitro-in vivo passage technique described by Twentyman et al. (17). Solid tumors were produced by subcutaneous injection of 105 cells in 0.1 ml of media into the shaved right flanks of female C3H/Anf mice. The in vivo tumors grow to a suitable size (1.0-1.5 cm in diameter) in about 14-21 days. Tumor volume was estimated by calculating the volume of an ellipsoid from the equation V = (r/6)a2b, in which a and b represent major and minor axes dimensions.Mice were anesthetized with 0.5% (vol/vol) halothane