18 consecutive patients with acute myeloid leukaemia (AML) treated with 34 cycles of intensive chemotherapy received ondansetron as antiemetic treatment. 14 patients were chemotherapy-naive, while 4 patients were treated for relapsed leukaemia. All patients received at least one cycle of chemotherapy, 11 patients (61%) received two cycles and 5 patients (28%) received three cycles. The remission induction regimen consisted of cytarabine 200 mg/m2 daily from day 1 to day 7, in combination with an anthracycline or amsacrine on 3 days. During the second and third cycle the dose of cytarabine was increased. Ondansetron was administered as follows: 8 mg intravenously before the start of chemotherapy, followed by 8 mg orally three times daily for 10 days. 50% of patients had no episodes of vomiting during the first cycle of chemotherapy and 78% had less than five episodes of vomiting over 10 days. 72% of patients had no or only mild nausea. These high response rates were maintained during the subsequent cycles. No side-effects due to ondansetron were registered. These data indicate that ondansetron is efficacious in preventing nausea and vomiting in patients with AML treated with intensive chemotherapy.