We performed a clinical evaluation on the antiemetic profile and the plasma concentration of Azasetron Hydrochloride (a new selective 5-HT3 receptor antagonist), in transcatheter arterial chemoembolization using CDDP for unresectable hepatocellular carcinoma. Antiemetic effects were examined in 32 patients in the serotone group (administration of serotone 10 mg + methylprednisolone 125 mg) and in 77 patients of the control group (administration of metoclopramide 20-30 mg + methylprednisolone 500 mg). The response rate and the CR ratio in serotone group was 97% and 66%, respectively. These results were statistically higher than in the control group. Although all patients had chronic liver diseases, no side effects and complications related to administration of serotone were observed. The average area under the concentration (AUC) curve of plasma serotone in five patients with liver cirrhosis was 531 ng.h/ml, which was greater than that of a healthy volunteer. In conclusion, serotone is a new, safe and useful antiemetic drug in TACE therapy for hepatocellular carcinoma.