Significant progress has been made in recent years in developing more effective means of preventing nausea and vomiting induced by cancer chemotherapy. With appropriate application of currently available antiemetic regimens, the majority of patients with cancer who are receiving chemotherapy can anticipate experiencing no emesis during their treatment. Nevertheless, incompletely controlled emesis remains a problem for a significant percentage of patients. Persistent challenges include delayed emesis and emesis following high-dose chemotherapy regimens. The goal of complete prevention of emesis in all patients remains elusive. Therefore, there is a strong rationale for investigating new antiemetic approaches. New antiemetic agents currently under development target the neurotransmitters serotonin (5-hydroxytryptamine; 5-HT) and substance P. A number of new selective antagonists of serotonin 5-HT3 receptors are in clinical trials. Given the lack of clinically significant differences between the available 5-HT3 receptor antagonists, it appears unlikely that any of these new agents will have substantial advantages over currently approved agents. Several other serotonin receptors have been targeted including the 5-HT4, 5-HT1A and 5-HT2A receptors. Of these approaches, only agonism of the 5-HT1A receptor has produced an agent that has proceeded into clinical testing. The most exciting new class of antiemetics currently under development focuses on antagonism of the effects of the neurotransmitter substance P. Results of early clinical trials with tachykinin neurokinin NK1 receptor antagonists demonstrate enhanced control of acute emesis with their addition to currently available agents and promising activity in controlling delayed emesis. Available evidence would strongly suggest that this class of agents will represent the next important advance in efforts to control nausea and vomiting induced by chemotherapy.