Clofarabine, a nucleoside analogue for treatment of relapsed leukemia, is 50-60% excreted in urine. Clofarabine has not been studied in patients on hemodialysis. We measured levels in one patient in acute renal failure. Prior to dialysis, 43 hr after a 40 mg/m(2) infusion, plasma concentration was 139 ng/ml. One hour after beginning hemodialysis, a 20 mg/m(2) infusion began. Plasma concentrations were 84.2, 81.1, and 88.0 ng/ml while the dialysis and clofarabine infusion occurred simultaneously. Post-dialysis, while the clofarabine was still infusing, the level was 95.8 ng/ml. Hemodialysis does decrease clofarabine levels, but given its large volume distribution, hemodialysis may not be effective for clofarabine overdose.