Mice fed for 15 days with Deuterium-Depleted Water (30 ppm deuterium) had a statistically significant increased survival rate compared with control groups fed with normal distilled water (150 ppm deuterium), after 8.5 Gy irradiation (61% survival in the test group versus 25% in the control group). The hematological picture showed that normal WBC, RBC and platelet counts were maintained in the test groups. Immunological parameters (serum opsonic and bactericidal capacity, bactericidal capacity of the peritoneal macrophages) showed a marked increase in the test groups compared to a severe decrease in the control groups. Auxiliary tests using chemical radiomimetics (hydrochloric embihine) and immunosuppressors (cyclophosphamide) showed a strong protective effect of deuterium-depleted water against the decrease of the leukocyte counts and other immunologic parameters. In conditions of experimental inflammation induced with subcutaneous-implanted pellets, deuterium-depleted water feeding resulted in a statistically significant increase of the inflammatory response, demonstrated by increased percentages of PMN and lymphocytes in the peripheral blood and the increased phagocytic capacity of the peripheral blood PMN. Experimental infections induced with K. pneumoniae 506 and S. pneumoniae 558 in mice irradiated or treated with cyclophosphamide showed increased, non-specific immunity parameters. All results show a marked intensification of the immune defenses and increased proliferation of the peripheral blood cells, probably accounting for the radioprotective effects.