Immunofluorescent labeling of adult mouse bone marrow cytospin preparations with anti-runt box antiserum in combination with MoAbs specific for granulocytes (anti-Gr-1; A and B) and erythroid cells (TER-119; C and D) or with an antiserum against B lymphocytes (anti-mouse Ig; E and F ). The anti-runt box reactivity appears as red-orange (R-phycoerythrin); reactivity with lineage-specific antibodies appears in green (FITC). The anti-runt box was competed with GST (anti-rbox + GST; A, C, and E) or with GST/runt (anti-rbox + GST/runt; B, D, and F ). Double-positive cells in (A), (C), and (E) are indicated by arrows.