The antiemetic activity of ondansetron (Zofran, Glaxo Pharmaceuticals, Research Triangle Park, NC) was evaluated in 25 patients with recurrent melanoma who were treated sequentially with dacarbazine (DTIC), vinblastine, and cisplatin. The antiemetic regimen included ondansetron alone in 11 patients; ondansetron plus lorazepam (Ativan, Wyeth-Ayerst, Philadelphia, PA) in 9 patients; and ondansetron plus lorazepam plus metoclopramide (Reglan, A. H. Robins Co., Richmond, VA) in 5 patients. Twenty-one patients had no prior exposure to chemotherapy, whereas 4 patients had previously received the same chemotherapy regimen and had severe vomiting despite administration of standard antiemetics. The antiemetic efficacy of ondansetron was impressive. Administration of a single dose of 10 mg resulted in complete control of nausea and vomiting in 22 patients, and the remaining 3 patients had only mild vomiting. Ondansetron is highly effective in controlling the nausea and vomiting caused by dacarbazine.