This report of a double-blind, randomized study performed to evaluate the comparative antiemetic efficacy of tropisetron (Navoban; Sandoz Pharma Ltd, Basel, Switzerland), a new 5-hydroxytryptamine receptor antagonist, focuses on treatment during stages of chemotherapy when nausea and vomiting are particularly severe. One hundred fifteen chemotherapy-naive patients with malignant disease were administered either tropisetron (n = 58) or a dexamethasone dose plus a metoclopramide dose (n = 57) during 5 days of two successive cycles of chemotherapy. Within the first 24 hours after receiving cisplatin-based chemotherapy, 76% of patients in the tropisetron group remained free of vomiting (with 59% of patients free of nausea) compared with 39% of patients free of vomiting in the conventionally treated group (30% of patients free of nausea). Improved control of emesis also was observed over 4 consecutive days of follow-up in the tropisetron group. The difference in incidence of nausea and vomiting between the patient groups was statistically significant (P < .05). The efficacy of tropisetron was well maintained during the second consecutive chemotherapy cycle; during the first 24 hours, 72% and 62% of patients remained free of vomiting and nausea, respectively. Tropisetron appears to be a highly effective, well tolerated, and simple to use antiemetic agent for patients receiving chemotherapy.