Leukapheresis is a common procedure for hematopoietic cell transplantation in adults. The main challenge in applying this procedure to human infants and small monkeys is the large extracorporeal blood volume (165 mL on average) necessary for priming the apheresis machine. This volume represents greater than 50% of the total circulating blood volume of a human neonate or small monkey. In this report, we document a safe leukapheresis protocol developed for rhesus macaques (3.9 to 8.7 kg). To avoid sensitizing donor animals undergoing leukapheresis to third-party blood products, autologous blood collected during the weeks prior to leukapheresis was used to volume-expand the same donor while priming the machine with saline on the day of leukapheresis. During the procedures, blood pressure was controlled by monitoring the inlet volume, and critical-care support was provided by the anesthesia team. Electrolytes and hemogram parameters were monitored intermittently. Overall, our research subjects underwent effective 4- to 6-h leukapheresis. A total of 9 leukapheresis procedures were performed, which yielded 1 × 10(9) to 6 × 10(9) peripheral blood mononuclear cells containing 1.1 to 5.1 × 10(6) CD34(+) cells (assessed in 4 of 9 macaques) in a volume of 30 to 85 mL. All macaques showed decreases in Hct and platelet counts. In summary, we report a successful modified leukapheresis procedure that can be performed safely in small animals without modification of the leukapheresis machine or associated cell-collection kits.