Mll5^−/− bone marrow cells show increased susceptibility to myelosuppression. Survival of Mll5^−/− and wild-type littermate control mice (21 per group) that received weekly intraperitoneal doses of 5-fluorouracil (5-FU; 200 mg/kg). Mll5^−/− mice showed significantly increased sensitivity to 5-FU (log-rank nonparametric test; P < .0001).