Background. Aprepitant is a P/neurokinin-1 receptor antagonist approved for the prevention of CINV in moderate emetic risk chemotherapy. We explored its effectiveness in patients with leukemia receiving cytarabine-based chemotherapy. Methods. Patients were randomized to ondansetron (OND) 8 mg IV 30 minutes before cytarabine followed by 24 mg IV continuous infusion daily until 6-12 hours after the last dose of chemotherapy alone or with aprepitant (APREP) oral 125 mg 6-12 hrs before chemotherapy and 80 mg daily until 1 day after the last dose of chemotherapy. Results. Forty-nine patients were enrolled in each arm; 42 in OND and 41 in OND + APREP arm were evaluable for efficacy. The ORR with OND + APREP was 80% compared to 67% with OND alone (P = 0.11). On days 6 and 7, higher proportion of patients treated with OND + APREP were free from nausea (74%, 74% versus 68%, 67%; P = 0.27 and 0.18, resp.). Requirement of rescue medications on days 2 and 3 was fewer in OND + APREP arm 7% and 5% compared to 21% and 16% in the OND arm, respectively (P = 0.06 and P = 0.07). Conclusions. There was a trend for overall improvement in emesis with ondansetron plus aprepitant. The potential benefit of this approach with specific chemotherapy combinations remains to be determined.