Fire is a key factor in the temperate semiarid region of central Argentina. The objectives of this work were to evaluate the effect of different fire intensities applied during different seasons under field conditions on the mortality of Piptochaetium napostaense (Speg.) Hack., Stipa tenuis Phil., and Stipa gynerioides Phil., 3 of the dominant grasses within the region and to determine their thermal death points in the laboratory. Ten plants of each species were exposed to low fire intensity (300-400 degrees C), high fire intensity (500-600 degrees C), and no fire (control) in April and December 1994, May 1995, and January 1996. Fire treatments were applied with a portable propane plant burner. The thermal death point was determined (during fall and spring) using the Wright's technique. Although mortality with high fire intensity was always higher than mortality with low fire intensity for all species, differences were not significant (p > 0.05). Pooling both treatments, the highest (p 0.05) for all burning dates. Only after the May burn, was average mortality of P. napostaense and S. tenuis higher (p < 0.05) than average mortality of S. gynerioides. The thermal death point was similar in all studied species. It was 65 degrees C during the fall, and 68 degrees C during the summer. This could explain, at least in part, similar mortalities (except after the May burn) between species and the date of burning found in this study. DOI:10.2458/azu_jrm_v54i5_pelaez