The clearance of 2-chlorodeoxyadenosine (2-CdA) in patients with renal insufficiency has not been characterized previously. The authors describe the clinical course and the pharmacokinetics of 2-CdA in a child with acute monoblastic leukemia who experienced acute renal failure during treatment with cytarabine and 2-CdA. 2-CdA (9 mg/m2 per day) was infused over 30 minutes daily for 5 days. Plasma and dialysate concentrations of 2-CdA were measured by high-performance liquid chromatography. The rate of this patient's 2-CdA clearance was lower than the rates reported for children with normal renal function. The average clearance rate, reflecting systemic clearance and clearance by continuous venovenous hemofiltration and hemodialysis, was 12.4 L/hour per m2 for the first 3 days of 2-CdA therapy. He did not experience untoward hematologic toxicity. Because high 2-CdA plasma concentrations were observed in this patient, clinicians are advised to exercise caution when using this drug in patients with renal dysfunction. More experience in the administration of 2-CdA to patients with renal insufficiency will be necessary to determine the need for dosage adjustment.