To evaluate the expression of cytoplasmic CD79a (CyCD79a) and other commonly used B-lymphoid immunomarkers including cytoplasmic CD22 (CyCD22), CD19, CD20 and CD10 in various acute leukemia cells and to define the most sensitive and specific markers in the diagnosis of precursor B-cell acute lymphoblastic leukemia (pB-ALL), the immunophenotypic data from 221 de novo adult and pediatric acute leukemia patients as studied using multi-parameter flow cytometry in addition to routine morphologic and enzyme cytochemical assay, were retrospectively analyzed. Cytogenetic and/or molecular biological data in all 45 cases of acute promyelocytic leukemia (APL) and 13 cases of acute leukemia suspected as AML with the fusion genes such as AML1/ETO and CBFbeta/MYH11 were investigated. The results showed that CyCD79a and CyCD22 were the most sensitive and specific markers respectively for pB-ALL. Expression of CyCD79a was seen in 100% of 58 cases of pB-ALL. At the same time, none (0%) of all 147 cases of acute myeloid leukemia (AML) and 15 cases of precursor T-cell acute leukemia (pT-ALL) was positive for CyCD22. The conclusion is made that united detection of CyCD79a and CyCD22 is the optimal immune combination for the diagnosis pB-ALL and the distinguishing pB-ALL with AML and pT-ALL.