in this article we describe the use of bench-scale single-fiber dialyzers for the development and testing of an immobilized enzyme reactor for the treatment of leukemia. the treatment is based on the enzymatic removal of specific amino acids from the blood of leukemia patients. l-lysine $alpha$ -oxidase and catalase were coimmobilized within the void space of the porous region of asymmetric hollow-fiber membranes for the removal of l-lysine from simulated human plasma solutions. hollow-fiber reactor performance was evaluated using a small single-fiber dialyzer (sfd) consisting of a single fiber encased in a protective glass shell. this small reactor affords ease of use, requires small amounts of chemicals and biochemicals, and gives useful reactor performance data. single-fiber dialyzers were constructed using polyamide fibers with a molecular weight cutoff of 10,000 (pa10 fibers); these fibers demonstrated the best compatibility with and retention of the enzymes. the sfd performance in removing l-lysine from solution was evaluated under both steady and pulsatile flow operation. (edited author abstract) 31 refs