Ondansetron: a new entity in emesis control. Nausea and vomiting are serious problems for patients receiving cancer chemotherapy. Dopamine receptor and cholinergic receptor antagonism have been the target mechanism for agents used to combat drug-induced nausea and vomiting; more recently, blockade of serotonin receptors has been used for this indication. Current therapies are limited by extrapyramidal adverse effects, as well as drowsiness, sedation, respiratory depression, and cardiac effects. Ondansetron is an investigational serotonin antagonist that has documented effectiveness for cancer chemotherapy-induced emesis. Ondansetron appears to be well tolerated, with the possible exception of headaches and transient increases in liver enzymes. No extrapyramidal toxicities have been reported with this agent. While ondansetron looks promising, further studies are needed to fully define its role as an antiemetic. 