Maropitant (Cerenia; a novel, selective neurokinin1 receptor antagonist), chlorpromazine, metoclopramide and ondansetron were compared in two randomized, placebo-controlled studies for efficacy in preventing emesis induced by emetogens acting centrally (apomorphine; Study 1) or peripherally (syrup of ipecac; Study 2) in dogs. In each study, ten male and ten female beagles were treated in a five-treatment, five-period crossover design. The five treatments were 0.9% saline (0.1 mL/kg), maropitant (1 mg/kg), metoclopramide (0.5 mg/kg), or chlorpromazine (0.5 mg/kg) all administered subcutaneously, or ondansetron (0.5 mg/kg) administered intravenously. One hour posttreatment dogs were challenged with apomorphine at 0.1 mg/kg intravenously (Study 1) or syrup of ipecac at 0.5 mL/kg orally (Study 2). Following emetogen challenge, dogs were observed for 30 min (Study 1) or 1 h (Study 2) for emesis. No clinical signs, other than those related to emesis, were observed. Efficacy of maropitant in preventing emesis induced centrally by apomorphine was not different (> 0.05) from metoclopramide or chlorpromazine but was superior (< 0.0001) to ondansetron. Efficacy of maropitant in preventing emesis induced by syrup of ipecac was not different (> 0.05) from ondansetron but was superior ( 0.0102) to metoclopramide or chlorpromazine. Maropitant was effective (< 0.0001 relative to control) in preventing vomiting caused by stimulation of either central or peripheral emetic pathways, whereas the other drugs examined prevented vomiting caused by central (metoclopramide and chlorpromazine; < 0.0001) or peripheral (ondansetron; < 0.0001) stimulation but not both.