Abstract The combined effects of water-bath hyperthermia at 42.5°C for 30 min, 1 10 LD 50 Bleomycin iv, and 200 rad x irradiation were studied in DDD strain male mice with Ehrlich ascites tumor. The objective was to acquire data on the optimum regimen for a combined administration of these three modalities. The treatments were given 10 days after the inoculation of 2 × 10 6 of the cells into the right hind limb. Concomitant application of the three modalities led to an 80% regression. A single modality produced no significant effect and a 30–50% regression occurred when only two modalities were combined. To assess the influence of timing and sequence, hyperthermia was applied at 1, 2, 4, and 6 hr before, after, or simultaneously with the combination of Bleomycin and 200 rad X ray. A significant effect was obtained in the case of concomitant application of the three and hyperthermia was effective when applied within 2 hr before or after administration of Bleomycin plus irradiation. This enhancement disappeared at 4-hr intervals.