Using appropriate standards immune flow cytometry permits quantitative analysis of the expression levels of cellular antigens. This information can be gained on an absolute basis and reported in terms of numbers of molecules per cell. This offers clues for reaching time-to-time and lab-to-lab comparability of immuno-fluorescence data. After briefly reminding the characteristics of available standards this paper provides an overview of the main relevant candidate molecules for flow cytometric quantitation on hemopoietic cells and reviews the major fields of application in immuno-hematology.