The inhibitory effect of ramosetron hydrochloride (Ram), a 5-HT3 receptor antagonist, on nausea and vomiting occurring in CMF or CEF therapy as a pre- or postoperative adjuvant chemotherapy or chemotherapy for recurrent cancer was evaluated in 34 patients with breast cancer. On days 1 and 8, the patients received Ram (0.3 mg) concomitantly with these agents intravenously and were observed for nausea and vomiting to evaluate the inhibitory effect. Food intake was observed at the same time. On day 1, there was moderate to severe nausea in one patient and vomiting in two patients, while results for 32 of 34 patients (94.1%) were classified as "excellent". On day 8, no moderate or severe nausea was seen, but vomiting occurred in one patient; the results of 33 patients (97.1%) were classified as "excellent". Even when considering only 12 patients who had experienced nausea or vomiting on chemotherapy, 11 showed an "excellent" response on day 1. Moreover, no patient received any additional dose of an anti-emetic drug within 24 hours of Ram administration. Food intake decreased to less than 50% of the baseline in three patients on day 1 and four patients on day 8. Administration of Ram to breast cancer patients on CMF or CEF therapy is thus concluded to be useful in the inhibition of nausea and vomiting.