Two-color staining to screen hybridomas for MoAb to CD34. Ficolle-separated BMMC were stained as described in the Materials and Methods. Cells were first incubated with hybridoma supernatants, washed, and then incubated with RPαCD34. Second-stage goat antirabbit PE and goat antimouse FITC antibodies were added simultaneously. Gates were drawn to exclude debris and to include cells with light scattering properties of lymphocytes and blasts. RPαCD34-PE staining is shown on the Y axis and staining of the MoAb-FITC on the X axis. MoAbs in (B), (C), and (D) give positive staining of the population of cells recognized by RPαCD34 as compared with 31A (control), which does not costain the CD34⁺ cells.