Sigmodon hispidus, a cotton rat, was inoculated with tachyzoites or oocysts of Costa Rican strains of Toxoplasma gondii to demonstrate the resistance to this parasite, as compared with mice, hamster and white rat infection. Susceptibility to tachyzoite inoculation was higher in this animal than in white rats but lower than in the other animals. Independent to the Toxoplasma strain studied, oocyst infection was less lethal for S. hispidus when compared with mice and hamsters; the results were similar to those observed for white rats. There is a probable participation of this wild animal in the natural Toxoplasma life cycle.