Maropitant is a neurokinin-1 inhibitor that acts to prevent and treat vomiting by blocking stimuli to the final common pathway in the emetic centre of the brain. The field efficacy and safety of a single oral dose of maropitant were investigated for the prevention of vomiting in dogs with a history of motion sickness resulting from transportation by car in two blinded, placebo-controlled studies. In an exploratory study designed as a two-way crossover trial with 17 dogs, 10 of the dogs given the placebo vomited during a car journey but only three of the dogs vomited under maropitant treatment. In a larger multicentred parallel design study, 69 of 105 dogs treated with the placebo vomited during the journey compared with 15 of 106 dogs treated with maropitant (P < 0.0001).