The present invention relates to kits and methods for performing dual-staining immunohistochemistry (IHC) for the detection of specific cell populations in tissue samples containing heterogeneous populations of cells, which can be observed by a light microscope for co-localization of distinct pigments. The method includes providing a tissue sample comprising fixed cells; exposing the sample to first and second ligands that recognize different marker proteins found at the same cellular location, thereby forming a ligand-labeled sample; exposing the ligand-labeled sample to first and second labeling reagents, the first labeling reagent binding to the first ligand and the second labeling reagent binding to the second ligand, the first and second labeling reagents each forming distinct pigments; and identifying the number of cells that display only one particular pigment, or more than one pigment, by the different coloration of the cellular location labeled by the distinct pigment.