This ready to use negative control reagent contains purified, fluorescein or phycoerythrin conjugated mouse immunoglobulin molecules of IgG1 isotype, which have been selected on the basis of their binding characteristics: no specific binding to human cell surface or intracellular antigens, same low range of nonspecific binding to human leukocytes as other Nordic-MUbio Reagents. This isotype control IgG1 is suitable as a Negative Control to be used in combination with Nordic-MUbio reagents for the: - Enumeration of Myeloid Cells - Analysis of Myeloid Differentiation Stage - Enumeration of B-cells and Precursors - Enumeration of T-cells and Precursors - Analysis of Leukemia Cells - Analysis of Immunodeficiency States The negative control reagent permits to estimate the degree of non-specific binding of isotype matched immunologbulins to leukocytes via e.g. Fc-receptors. It enables the expert to set flow cytometric parameters accordingly. Results must be put within the context of other diagnostic tests as well as the clinical history of the patient by a certified professional before final interpretation.