ZCH-2B8a (IgG2a) is a novel monoclonal antibody (McAb) generated in laboratory of Children Hospital of Medical College, Zhejiang University recently using human myeloblastic leukemia cell line KG1a as immunogen. This antibody has been submitted to the 8th International Workshop and Conference on Human Leukocyte Differentiation Antigens (HLDA8) and the results showed that the antibody recognized an unknown molecule on the surface of some blood cells. The aim of this study was to investigate the reactivity of this antibody on normal blood cells and malignant cell lines and to explore its possible application in clinical practice. The multi-parameter flow cytometry was used to analyze the expression pattern of 2B8a antigen in triplicate on normal blood components including T cells, B cells, natural killers (NK), neutrophils, monocytes, dendritic cells (DC), red blood cells (RBC), platelets (Plt), hematopoietic stem/progenitor cells derived from either bone marrow or G-CSF mobilized peripheral blood CD34(+) cells and malignant cell lines including 14 hematopoietic, 5 neuroblastoma, 1 colon cancer and 1 amniotic epithelium cell lines. The amount of positive cells > or = 20% was considered as positivity. The results showed that 2B8a antibody reacted to 3/3 specimens of blood B cells with a positive rate of 26.29% and 2/3 specimens of monocytes with an average positive rate of 59.84%. 2B8a was weakly reactive to neutrophils (23.72%) and negative for T cells, NK, DC, RBC and Plt. The antibody reacted to all 3 marrow CD34(+) cells with an average positive rate of 39.33% while it was negative for G-CSF-mobilized CD34(+) peripheral blood stem/progenitor cells (PBSC, 1.25%). Cell line analysis showed that the antibody notably reacted to three out of 4 cell lines (Raji, SMS-SB, Nalm-6 and Nall-1) with the positive rates of 98.78%, 98.61%, 94.93% respectively and weakly to one of them with 5.68% in B lineage cell lines and monoblastic cell line (U937, 67.78%) while it was only weakly positive or negative for other myeloid leukemia cell lines including Meg01 (33.40%), HL-60 (29.70%), K562 (28.19%), KG1a (16.23%) and HEL92.1.7 (8.02%). Among 4 T lineage leukemia, 5 neuroblastoma and 1 colon cancer cell lines tested, only Molt-3 was found weakly positive (31.40%) for 2B8a, while the remaining 3 T cell lines (Molt4, JM and CCRF-CEM), 5 neuroblastoma cell lines (LA-N1, KCNR, BE, SK-N-SH, SK-N-AS) and the colon cancer cell line (HR8348) tested were negative. An amniotic epithelium cell line (FL) was showed positive for the antibody (45.03%). It is concluded that 2B8a antibody primarily reacts to B lineage and monocytic lineage cells which may bear the diagnostic and therapeutic applications among different types of hematopoietic malignancies.