OUTLINE: This study seeks to estimate the maximum tolerated dose (MTD) of yttrium-90-labeled humanized monoclonal antibody M195 (90Y-MOAB HuM195). All patients receive a single intravenous dose of 90Y-MOAB HuM195. Groups of 3 to 6 patients are treated at escalated doses of yttrium-90 until the MTD is determined. Patients with active leukemia who exhibit at least a 50% clearing of marrow blasts after the first dose may receive a second dose after 4-8 weeks provided remaining blasts are CD33-positive, there is no evidence of human anti-human antibody response, and any toxicity has resolved. All patients are followed monthly for 4 months after treatment.