[en] The intracellular parasite Toxoplasma gondii (Apicomplexa), has as definitive host domestic and wild felines and as intermediate hosts most species of mammals and birds, Including man. The infection in man is usually asymptomatic, but can become a severe and lethal illness in some special groups like the fetus of primoinfected pregnant woman, or in AIDS and transplanted patients. The transmission is due to ingestion of food or water contaminated with oocysts from cat feces as well as raw or rare cooked cyst containing meet. There is no available vaccine against toxoplasmosis, with some reports of the use ionizing radiation in order to attenuate or suppress the parasite. These studies are promising, but more research is needed to optimize the radiation process and to clarify those alterations caused on T gondii.Using a increasing doses of ⁶⁰ Co irradiation on T.gondii tachyzoites, we studied many parameters such as morphology, both at optical and electron microscopy level, detection of DNA fragmentation, metabolism alterations (cellular oxidative burst, protein, nucleic acids and DNA synthesis), determination of the parasite survival both in in vivo and in vitro models, antigenicity and immunogenicity after the process, cellular invasion and irradiated tachyzoite induced protection. After definition of 200 Gy of ⁶⁰ Co irradiation as the lower radiation dose that suppress parasite growth in vitro and in vivo, we found no detectable changes in parasite viability, its cell invasion capacity or in its structural proteins. DNA fragmentation like apoptosis or alterations of the parasite metabolism were similarly not affected by radiation. Mice infection with irradiated parasites induce partial protection when these animals were re-inoculated with non irradiated virulent parasites, inducing greater specific IgG levels as well as a longer survival. Irradiated T.gondii maintains its the ability of invasion, even under radiation effects. Based on our results we conclude that ionizing radiation can be considered as a possible tool in vaccine production due to similar viability, invasivity and metabolism and absence of reproductive capacity, of irradiated tachyzoites. (author)