Folinic acid (FA) has been reported to expand the pool of peripheral blood stem cells (PBSC) after chemotherapy. We evaluated the efficacy of FA for harvesting PBSC following cytotoxic chemotherapy in 4 patients with acute leukemia. After achieving a complete remission (CR), 3 courses of chemotherapy for a consolidation of the CR were administered to the patients. Two successive cycles of leukapheresis were performed during the recovery phase from consolidation chemotherapy, which consisted of an intermediate dose of cytosine arabinoside. For the second cycle of leukapheresis, FA was administered intravenously at a dose of 50 mg/day following consolidation. The yields of either mononuclear cells or burst-forming units-erythroid (BFU-E) were not affected by FA administration. In contrast, the yields of colony-forming units-granulocyte/macrophage (CFU-GM) were significantly decreased in all patients compared to the CFU-GM yields after the first cycle of leukapheresis (P = 0.032). Thus FA is considered not to be effective in expanding the peripheral blood progenitor pool when given in a fashion different from the original report.