A method for labeling intracellular and extracellular targets of leukocytes, comprising the steps of: (a) forming a combination of (i) a cellular composition, comprising at least leukocytes and red blood cells, and (ii) a first solution comprising one or more agent(s) that are capable of cross-linking intracellular proteins, lipoproteins and nucleic acids of said leukocytes; (b) adding a second solution to said combination, comprising one or more agent(s) that are capable of permeabilizing said leukocytes, lysing said red blood cells and neutralizing the cross-linking activity of said one or more agent(s) in said first solution, wherein said second solution comprises (i) a detergent in an amount of 0.05% to 0.5% (w/v), and (ii) a quaternary ammonium salt or an amine containing compound in a concentration of 1 to 100 mM, wherein said second solution has a pH of 6.5 or lower and wherein the added volume of said second solution is between 1 and 10 times the total volume of said combination; (c) adding either concurrently with or subsequently to addition of said second solution at least one binding agent which specifically binds to an extracellular target of leukocytes, and at least one binding agent which specifically binds to an intracellular target of leukocytes, wherein each of said binding agents comprises a detectable agent; and (d) adding a third solution to said combination, wherein the added volume of said third solution is equal to or higher than the total volume of said combination to which the third solution is added, wherein said third solution comprises (i) a fixative selected from the group consisting of formaldehyde, paraformaldehyde, and glutaraldehyde, and (ii) a detergent. (a) forming a combination of (i) a cellular composition, comprising at least leukocytes and red blood cells, and (ii) a first solution comprising one or more agent(s) that are capable of cross-linking intracellular proteins, lipoproteins and nucleic acids of said leukocytes; (i) a cellular composition, comprising at least leukocytes and red blood cells, and (ii) a first solution comprising one or more agent(s) that are capable of cross-linking intracellular proteins, lipoproteins and nucleic acids of said leukocytes; (b) adding a second solution to said combination, comprising one or more agent(s) that are capable of permeabilizing said leukocytes, lysing said red blood cells and neutralizing the cross-linking activity of said one or more agent(s) in said first solution, wherein said second solution comprises (i) a detergent in an amount of 0.05% to 0.5% (w/v), and (ii) a quaternary ammonium salt or an amine containing compound in a concentration of 1 to 100 mM, wherein said second solution has a pH of 6.5 or lower and wherein the added volume of said second solution is between 1 and 10 times the total volume of said combination; (i) a detergent in an amount of 0.05% to 0.5% (w/v), and (ii) a quaternary ammonium salt or an amine containing compound in a concentration of 1 to 100 mM, (c) adding either concurrently with or subsequently to addition of said second solution at least one binding agent which specifically binds to an extracellular target of leukocytes, and at least one binding agent which specifically binds to an intracellular target of leukocytes, wherein each of said binding agents comprises a detectable agent; and (d) adding a third solution to said combination, wherein the added volume of said third solution is equal to or higher than the total volume of said combination to which the third solution is added, wherein said third solution comprises (i) a fixative selected from the group consisting of formaldehyde, paraformaldehyde, and glutaraldehyde, and (ii) a detergent. (i) a fixative selected from the group consisting of formaldehyde, paraformaldehyde, and glutaraldehyde, and (ii) a detergent.