We examined the anti-emetic effect, safety and usefulness of ondansetron hydrochloride, a selective 5-HT3 receptor antagonist, given orally once daily at the dosage of 4 mg, for 3 to 5 consecutive days to patients with nausea and emesis induced by non-platinum anti-cancer drugs such as cyclophosphamide, doxorubicin and carboplatin. Out of 84 cases where anti-emetic effects were evaluated, numbers of cases assessed as excellent and good were 36 (83.3%) and 34 (40.5%), respectively, the efficacy rate being 83.3% (70/84). Side effects, such as moderate constipation (3 cases) and mild headache (3 cases), were observed in 8/85 cases (9.4%). Abnormalities in clinical laboratory findings including elevation of hepatic function and uricacid values and increase in eosinocyte counts, were observed in 3/85 cases (3.5%). As to overall safety, 78/85 cases (91.8%) were evaluated as having no problem in safety, and 7/85 cases (8.2%), as having minor problem in safety. As to clinical usefulness based on anti-emetic effect and overall safety, out of 79 cases the drug was assessed as very useful in 29 cases (36.7%) and useful in 35 cases (44.3%), the rate of "useful" or above being 81.0% (64/79). Furthermore, when ondansetron was administered in 3 courses of chemotherapy, though the number of patients was small, it was shown that anti-emetic effect of ondansetron did not decline and no problem in safety was observed. From the above, ondansetron which exerted adequate anti-emetic effect in 4 mg once daily doses was considered as a useful and safe anti-emetic in treatment of nausea and emesis associated with cancer chemotherapy.