In a randomized, double-blind, crossover trial, nabilone was compared to prochlorperazine for control of cancer chemotherapy-induced emesis in 30 children 3.5 to 17.8 years of age. All subjects received two consecutive identical cycles of chemotherapy with the trial antiemetics given in accordance to a body weight-based dosage schedule beginning eight to 12 hours before treatment. The overall rate of improvement of retching and emesis was 70% during the nabilone and 30% during the prochlorperazine treatment cycles (P = .003, chi 2 test). On completion of the trial, 66% of the children stated that they preferred nabilone, 17% preferred prochlorperazine, and 17% had no preference (P = .015, chi 2 test). Major side effects (dizziness, drowsiness, and mood alteration) were more common (11% v 3%) during the nabilone treatment cycles. CNS side effects appeared to be dose related and were most likely to occur when the nabilone dosage exceeded 60 micrograms/kg/d, but individual tolerance to nabilone varied considerably. Lower dosages of nabilone were associated with equivalent efficacy and no major side effects. Nabilone appears to be a safe, effective, and well-tolerated antiemetic drug for children receiving cancer chemotherapy. Although major side effects may occur at higher dosages, nabilone is preferable to prochlorperazine because of improved efficacy.