Both tropisetron (0, 0.025, 0.1, 0.25, 1, and 5 mg/kg) and Δ9-THC (0, 0.1, 0.25, 0.5, 1 and 5 mg/kg) by themselves reduced the frequency of cisplatin-induced (20 mg/kg) emesis in a dose-dependent manner. Only low doses of Δ9-THC (0.25 and 0.5 mg/kg) in combination with low doses of tropisetron (0.025 and 0.1 mg/kg) had significantly greater antiemetic efficacy in reducing the frequency of emesis relative to corresponding vehicle-treated tropisetron control groups. *Significantly different from 0 mg/kg Δ9-THC control group for the corresponding doses of tropisetron, p<0.05. ▼ Significantly different from the corresponding tropisetron vehicle control group, p<0.05.