The emetic responses to various pharmacological agents, cytotoxins, and radiation are compared among animal species. The species included for comparison are the human, nonhuman primate, dog, cat, and ferret. The categories of pharmacologic compounds include both those compounds that act on identified membrane receptors (e.g., cholinergic agonists, catecholamines, and neuroactive peptides) and those that act on unidentified receptors (e.g., cardiac glycosides and Veratrum alkaloids, among others). Emphasis is placed on emetic dose-response relations and threshold ED50 and ED100 values calculated from these relations, as indices of species sensitivity to emetic stimuli. For the more noxious emetics, the cytotoxins and radiation, the latency to the first emetic episode and duration of emesis are also compared across species. The effect that peripheral and central nerve lesions have on species differences in emetic responses to stimuli is also discussed.