Cisplatin was administered at a dosage of 50 mg/m2 of body surface to 69 dogs with various neoplasms. Dogs were randomly assigned to receive antiemetics according to 1 of the following 5 protocols: group 1, no antiemetic (control, n = 45 treatments); group 2, 0.4 mg of butorphanol/kg of body weight (n = 52 treatments); group 3, 0.2 mg of butorphanol/kg (n = 19 treatments); group 4, 2 mg of cyproheptadine/kg (n = 48 treatments); and group 5, 1 mg of cyproheptadine/kg (n = 10 treatments). Randomization was performed for each dog prior to each treatment. Butorphanol was administered IM immediately after completion of cisplatin infusion. Cyproheptadine was given orally 12 to 14 hours before and again immediately before cisplatin administration. The proportion of dogs that vomited in group 1 was 40 of 45 (89%). Butorphanol at a dosage of 0.4 mg/kg proved highly effective in preventing cisplatin-induced vomiting, reducing the proportion of dogs that vomited (10/52, 19%) compared with the control group.