In order to develop a non‐isotopic quantitative assay of granulocyte colony‐stimulating factor (G‐CSF) receptors on human or murine cells, we devised a flow‐cytometric assay using cells stained with biotin‐labelled G‐CSF (b‐G‐CSF) and a streptavidin‐RED670 conjugate. For quantification, we applied the Kolmogorov‐Smirnov test and calculated the D value. The D value was evaluated from the degree of shift in two fluorescence profiles according to the increase of fluorescence intensity due to the specific binding of b‐G‐CSF to G‐CSF receptors. A good correlation was observed between the number of G‐CSF receptors obtained by the radioisotopic binding assay and the number calculated from the D value by the flow‐cytometric assay. Then, expression of G‐CSF receptors on human bone marrow cells, peripheral blood granulocytes and blast cells from patients with acute myeloid leukaemia (AML) were studied. G‐CSF receptors was expressed on CD34⁺CD33⁻, CD34+CD33+ and CD34⁻CD33+ cells in the following order: CD34 CD33⁺CD34⁺CD33⁺CD34⁺CD33 cells, indicating that the receptors increased with maturation. The receptor levels of CD34⁻CD33⁺ cells in bone marrow were apparently lower than those of CD34⁻CD33⁺ cells in peripheral blood granulocytes. On the other hand, an abnormal expression pattern of G‐CSF receptors was noted in AML blast cells.