A composition comprising: A. a first antibody labelled with a first fluorochrome having a first emission spectrum, said first antibody that binds to an antigenic determinant that is differentially expressed on populations of leukocytes and non-leukocytes in said sample; B. at least one additional antibody, selected from the group consisting of: i) an additional antibody labelled with said first fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and ii) an additional antibody labelled with an additional fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and wherein said additional fluorochrome has an emission spectrum distinguishable from said first emission spectrum, and (iii) an additional antibody labelled with an additional fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and wherein said additional fluorochrome has an emission spectrum that overlaps said first emission spectrum; and C. a nucleic acid dye which has a peak emission spectrum that overlaps with the peak emission spectrum of at least one of said first emission spectrum or said additional emission spectrum. A. a first antibody labelled with a first fluorochrome having a first emission spectrum, said first antibody that binds to an antigenic determinant that is differentially expressed on populations of leukocytes and non-leukocytes in said sample; B. at least one additional antibody, selected from the group consisting of: i) an additional antibody labelled with said first fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and ii) an additional antibody labelled with an additional fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and wherein said additional fluorochrome has an emission spectrum distinguishable from said first emission spectrum, and (iii) an additional antibody labelled with an additional fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and wherein said additional fluorochrome has an emission spectrum that overlaps said first emission spectrum; and i) an additional antibody labelled with said first fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and ii) an additional antibody labelled with an additional fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and wherein said additional fluorochrome has an emission spectrum distinguishable from said first emission spectrum, and (iii) an additional antibody labelled with an additional fluorochrome, wherein said additional antibody binds to an antigenic determinant that is differentially expressed on populations of mature and immature granulocytes or myeloid cells, and wherein said additional fluorochrome has an emission spectrum that overlaps said first emission spectrum; and C. a nucleic acid dye which has a peak emission spectrum that overlaps with the peak emission spectrum of at least one of said first emission spectrum or said additional emission spectrum.