PI-6 is expressed in peripheral blood monocytes and granulocytes. Leukocytes from fresh, normal peripheral blood were analyzed by FACS after staining for PI-6 and CD14. The left-hand panel shows a scatter plot of the distribution of leukocytes into the small lymphocyte (R1) and monocyte/granulocyte (R2) populations. The central and right hand panels show the results of two-color FACS analysis of the R1 and R2 populations simultaneously stained with the anti–PI-6 monoclonal antibody 3A (x-axis) and an antibody recognizing the monocyte/granulocyte differentiation antigen CD14 (y-axis). The R1 population is not significantly marked by either antibody, whereas the R2 population is stained by both.