In recent years a new class of agents, the serotonin type 3 receptor antagonists, has been identified. This article reviews the preclinical, pharmacological and clinical data of ondansetron, granisetron and tropisetron, the first representatives of this group. Preclinical work showed that the drugs interfere with a variety of physiological processes, and hold promise for clinical utility in a wide range of areas. To date, these agents have proven, both in early clinical and comparative studies, to be potent antiemetic agents in patients receiving cisplatin and non-cisplatin chemotherapy as well as radiotherapy. In comparative studies the antiemetic efficacy mostly has been superior to conventional antiemetic drugs with regard to the acute chemotherapy-related symptoms; whereas their role in delayed emesis needs further investigation. This also applies for their role as an antiemetic in other types of nausea and vomiting (post-operative). Toxic effects have been modest, no extrapyramidal reactions have been reported. Potential clinical use in psychiatric disorders has been suggested, and the results of clinical trials are awaited.