The object of this study was to investigate the efficacy of (+)-catechin, which was isolated from Actinidia arguta Planch (Actinidiaceae), as a bone marrow cell proliferation-promoting compound against the hematotoxicity of 5-fluorouracil (5-FU) in mice. Intraperitoneally injected (+)-catechin (1 and 10 mg/kg per day) accelerated the recovery of the number of white blood cells (WBC) and platelets (PLT) but did not affect the number of circulating red blood cells (RBC). (+)-Catechin also augmented the number of myelocytes and splenocytes. Dual color flow cytometric analysis revealed that (+)-catechin reversed the reduction of the population of leukocytes (CD11b(+) monocytes, Gr-1(+) granulocytes and CD3(+) T and CD45RA(+) B lymphocytes) in whole blood, spleen and bone marrow caused by 5-FU. (+)-Catechin (I and 10 mg/kg per day) showed remarkable recovery of Gr-1(+) cells in all three types of tissues and of CD11b(+) cells in the bone marrow cells. These findings suggest that (+)-catechin selectively enhances the recovery of the population of granulocytes reduced by 5-FU in mice. (C) 2004 Elsevier Ireland Ltd. All rights reserved.