The anti-emetic effect and safety in patients receiving ondansetron hydrochloride (OND group) and ondansetron and dexamethasone (DEX group) concurrently in cases of acute and delayed onset emesis induced by a single high dose of cisplatin, given as a chemotherapy to gynecological cancer patients, were comparatively studied. The study subjects were 139 gynecological cancer patients. The OND group received 4 mg of ondansetron via slow intravenous injection on Day 1, 30 minutes prior to cisplatin, and for Days 2 to 5, the subjects orally received 4 mg ondansetron tablet each day. The DEX group received the same dose regimen of ondansetron as the OND group for Days 1-5, but in addition the subjects received dexamethasone injection in doses of 8 mg twice daily on Day 1 and 4 mg (1 mg QID) daily for Days 2-5. An anti-emetic effect against acute nausea and vomiting was achieved in 47.9% of the OND group and in a higher rate of 84.2% of the DEX group. Significantly better efficacy was seen in the DEX group also in the complete suppression rate of nausea and vomiting and the improvement of food intake. The group also achieved better efficacy in delayed onset of emesis. Adverse reactions were observed in 2 cases (2 reports of headache) in the OND group and 5 cases (2 reports of hiccups, 2 headache, 2 diarrhea, one constipation, one hot facial flushes and one elevation of gamma-GTP) in the DEX group; however, since the symptoms were all mild, we did not consider there was any problem in safety. We conclude from the above findings that concurrent administration of ondansetron hydrochloride and dexamethasone is a clinically useful treatment for acute and delayed onset emesis induced by a single high dose of cisplatin given to gynecological cancer patients.