Antiemetic treatment should be considered for breast cancer patients receiving moderately emetogenic chemotherapy. Although the extent of chemotherapy-induced emesis is largely dependent on the emetogenic potential of the specific agents employed, patient characteristics such as age and sex also contribute. Recent clinical studies show that treatment with the currently available 5-HT3 antagonists effectively reduces the incidence of chemotherapy-induced nausea and vomiting and improves quality of life in a substantial number of these patients. A Medline search from 1994 through February 1998 identified clinical trials that included previously untreated breast cancer patients using antiemetic therapy such as granisetron, ondansetron, dolasetron, and metoclopramide. The studies reviewed here indicate that the antiemetic efficacy of 5-HT3 antagonists is equivalent in previously untreated patients receiving moderately emetogenic chemotherapy for breast cancer, depending on the doses and schedules utilized. In particular, two comparative studies of granisetron and ondansetron with specific data for breast cancer patients showed that both agents eliminate nausea in approximately 50%, and vomiting in 60-70% of these patients, with the higher values observed when steroids were added to the 5-HT3 receptor antagonist regimen. Although the chemotherapy regimens employed for breast cancer are considered only moderately emetogenic, these regimens account for 60-90% of patients experiencing nausea and vomiting. The most recent clinical studies demonstrate that 5-HT3 antagonists can significantly reduce the incidence of nausea in breast cancer patients receiving moderately emetogenic chemotherapy and should be employed in this setting.