We evaluated the efficacy and safety of ondansetron hydrochloride (OND) on nausea and vomiting during repeated courses of CHOP or ACOMP-B therapy in patients with malignant lymphoma. The impact of the prognosis announcement on the anti-emetic effect and chemotherapy-associated adverse events was also investigated. Forty-two subjects with malignant lymphoma who underwent CHOP or ACOMP-B therapy including cyclophosphamide 600 mg/m2 and adriamycin 40 mg/m2 were investigated for a maximum of 6 courses. For acute nausea and vomiting, ondansetron was injected intravenously before the start of chemotherapy on the first day of each course of chemotherapy. For delayed emesis, ondansetron was administered orally for 4 days from the following day. The efficacy on acute nausea and vomiting was found to be 95.0% (1st course), 95.0% (2nd course), 90.9% (3rd course), 88.2% (4th course), 92.3% (5th course) and 91.7% (6th course), respectively. A high efficacy of > or = 85% was also obtained for delayed nausea and vomiting on each day. Though the adverse event of elevated GPT value developed in one subject. It was mild and resolved. No difference in efficacy was seen with or without announcement of prognosis to patients. Following the investigation on antiemetic effect, patient perception of chemotherapy-induced adverse events was evaluated. The most common event was hair loss, followed by taste abnormality and numbness and hyposthesia of the tips of the fingers. The incidence of nausea and vomiting was the 4th and 5th most common, which are less frequent than in the report of Coates in 1983. In conclusion, ondansetron is considered clinically useful with stable anti-emetic effect on both acute and delayed nausea and vomiting over repeated courses of chemotherapy, without any significant safety problem.