We describe a newly-made murine monoclonal antibody to the common acute lymphoblastic leukemia antigen (CALLA), named SHB-10. The antigen detected by SHB-10 has a molecular weight of about 105 kDa. This antibody is very similar to that of conventional anti-CD10 Ab on indirect flowcytometric analysis using lymphoid malignant cell lines and peripheral lymphocytes of acute lymphoblastic leukemia (ALL) patients. The binding of anti-CD10 to Daudi cell and peripheral lymphocytes of ALL patients is blocked by SHB-10. Thus this monoclonal antibody is thought to detect the CALLA. The distribution of antigen detected by SHB-10 on several cell lines of neuroectodermal tumor and lymphoid malignancy was analysed and a slight difference in their cell surface expression is observed when compared with that by conventional anti-CD10. Further biochemical analysis is now under way for a better characterization of this antigen.