The introduction of 5-HT3 antagonists, such as ondansetron, as antiemetic agents has transformed the management of patients receiving chemotherapy or radiation therapy. Studies in animal models with NK1 antagonists suggest that these represent a new class of antiemetic agents having a broader spectrum of activity than 5-HT3 antagonists. Compounds of this class may prove to be more effective in man against delayed emesis induced by cisplatin, post-operative nausea and vomiting and motion sickness. Thus, they have the potential to complement 5-HT3 antagonists and so provide a further advance in the management of nausea and vomiting.