This study evaluated the potential use of the guinea pig as an animal model in conducting combusttion toxicology experiments i which lethality is the endpoint. The guinea pig was found to be approximately three times as sensitive as the rat upon exposure to hydrogen chloride, presumably due to its tendency for bronchoconstriction. Compared to the rat, the guinea pig was relatively insensitive to carbon monoxide. Lethal effects of mixtures of carbonmonoxide and hydrogen chloride showed additivity only at relatively high concentrations of carbon monoxide. The lethal toxic potency of hydrogen cyanide was about the same for both the rat and the guinea pig. Based on comparisons of available toxicity data for humans and nonhuman primates, it was concluded that the rat is the better model when lethality studies are used. However, it is uncertain which animal model would be better when sublethal exposures, particularly to irritants, are considered.