Using the VpreB-PE and the VpreB-FITC mAbs, 36 diagnostic cases were tested for VpreB surface expression in day 0 cryopreserved samples that were obtained from children and young adults with NCI standard- and high-risk B-ALL. Cases were subdivided into pro-B and pre-B-ALL based upon the absence or presence of coexpression with CD10 and CD20. There were no statistical differences in VpreB expression among these 3 subgroups, but all cases except 4 showed >20% expression using either the PE-conjugated (A) or the FITC-conjugated (B) CD179a mAbs. Lack of VpreB expression could not be correlated with the presence or absence of any recurring molecular aberrations, as shown in supplemental Table 2. Neg, negative; Pos, positive.