We evaluated, in a multi-center trial, the safety and efficacy of GR 38032F (GR-C507/75), a novel and selective serotonin antagonist, in preventing acute emesis in chemotherapy-naive patients receiving treatment with regimens containing high-dose cisplatin (greater than or equal to 100 mg/m2). Eighty-five patients were randomized to receive GR 38032F, 0.18 mg/kg, either every six or every eight hours for three doses, beginning 30 minutes before cisplatin. Patients were evaluated for emetic episodes (vomiting or retching) over a 24-hour period following cisplatin. All patients were evaluable for toxicity and 83 were evaluable for efficacy. The overall antiemetic response rate was 75% (55% complete response [CR], 20% major response). No difference in antiemetic control between the two administration schedules was noted. Patients with histories of heavy ethanol use had significantly better antiemetic control (74% CR) than modest or non-drinkers (33% CR). Toxicity of GR 38032F was modest and independent of administration schedule. The most common adverse events included mild hepatic transaminase elevations, self-limited diarrhea, dry mouth, headache, and mild sedation. Our data indicate that GR 38032F is a safe and effective agent in the control of acute cisplatin-induced nausea and vomiting. Additional trials exploring dosing, schedule, and comparison to standard antiemetic agents are indicated.