This study reports the effectiveness and side effects of intravenous ondansetron as a single-agent antiemetic therapy for patients receiving emetogenic cancer chemotherapy under a compassionate-use program for patients not enrolled in controlled clinical trials. Patients were > or = 7 years old and had uncontrolled nausea and vomiting or intolerable side effects with standard antiemetics administered with previous cancer chemotherapy. All patients received ondansetron 0.15 mg/kg every 4 hours x 3 daily doses beginning 30 minutes prior to emetogenic chemotherapy. Patients could receive ondansetron for up to 5 consecutive days of chemotherapy. One hundred ninety patients received ondansetron during chemotherapy treatments that were similar to previous cycles of chemotherapy during which the patients had received standard antiemetics (identical chemotherapy or differing only by addition/deletion of chemotherapy agents of low emetogenicity). Chemotherapy regimens included cisplatin (n = 99; 52%), doxorubicin (without cisplatin, n = 52; 27%), and other drugs (n = 39; 21%). Patient experiences with nausea and vomiting and side effects with ondansetron and with previous standard antiemetics were rated on a scale of 1 to 10 (1, did not experience; 10, as bad as could be). On the nausea and vomiting scale, 74% of patients improved on ondansetron relative to standard antiemetics. Mean nausea and vomiting scales were 3.9 for ondansetron and 7.7 for standard antiemetics (P < .001). On the side effects scale, 62% of patients improved with ondansetron. Mean side effect scores were 1.8 for ondansetron and 4.5 for standard antiemetics (P < .001). One hundred nine patients assessed the effect of nausea and vomiting on their quality of life by means of the Functional Living Index-Emesis. On a 100-point scale (100=best quality of life), quality of life scores were 65.5 for ondansetron and 39.5 for standard antiemetics (P < .01). Functional Living Index-Emesis scores were higher for 76% of patients during ondansetron treatment as compared with previous chemotherapy with standard antiemetic regimens. Twenty-eight patients (15%) were withdrawn from the study because of nausea and vomiting. Forty-four patients (23%) experienced other adverse effects (headache, 17 patients; diarrhea, eight patients; all other events occurred in two or fewer patients). Only six patients were withdrawn due to adverse effects. In conclusion, ondansetron therapy resulted in significantly improved control of nausea and vomiting, fewer side effects, and better quality of life than standard antiemetic therapy in the same patients receiving similar chemotherapy regimens.