The observed marked improvement in efficacy of hyperbaric oxygen (O2 3ATA) by pentobarbital anesthesia to increase the response of C3H mammary carcinoma to irradiation will be evaluated using a series of spontaneous tumors (importance of histology, tumor size, anesthetic agent, depth of anesthesia, fractionation pattern, body temperature, blood perfusion of tumor, etc.) The potential of combining chemical sensitizers of hypoxic cells with hyperbaric oxygen to improve results of radiation therapy will be investigated in murine tumors; the two sensitizers will be combined at dose or PO2 levels which independently have comparable enhancement ratios. A "head on" comparison of the Therapeutic Gain Factors for photons plus O2 3ATA, photons plus misonidazole, and fast neutrons using a spectrum of spontaneous tumors of the C3Hf/Sed mouse is to be performed. The phenomenon of heat induced thermal tolerance will be studied to determine its time course, magnitude, dependence upon severity of the inducing heat treatment, time between the two exposures. Biological characterization of 9 spontaneous tumors is to be completed.