We have used the ferret as an animal model to investigate the emetic action of the cytotoxic drugs cyclophosphamide and cis-platin. Using selective nerve lesions, a crucial role for the abdominal innervation in the genesis of retching and vomiting in response to these agents has been demonstrated. A combination of bilateral abdominal vagotomy and greater splanchnic nerve section can totally abolish retching and vomiting in response to intraperitoneal cis-platin or intravenous cyclophosphamide. Intraperitoneal cyclophosphamide still produced retching but vomiting was markedly reduced, demonstrating complex and probably separate control mechanisms for retching and vomiting. The effect of a widely used anti-emetic, metoclopramide, was compared to that of nerve lesions. While effective this compound did not totally control retching or vomiting to either drug. Recent studies have attributed metoclopramide's action to its ability to antagonize 5-HT M-receptors (5-HT-3 receptors). Therefore we investigated BRL 24924, a gastro-kinetic agent with more specific 5-HT M-receptor antagonist properties. This agent was extremely potent in almost totally abolishing retching and vomiting in response to cyclophosphamide, given by either an intravenous or intraperitoneal route, and totally abolished cis-platin-induced vomiting for at least 4 h. Clearly the abdominal visceral innervation plays a complex and major role in the emesis produced by these two cytotoxic drugs; circumstantial evidence suggests that 5-HT M-receptors on visceral afferent nerves mediate this action, but other possibly central sites of action of the 5-HT M-receptor antagonists cannot be excluded.