Conventional microscopic techniques may be easily employed to detect and characterize cytotoxic T lymphocytes (CTL). Immunohistochemistry (IHC) may be effectively performed in CTL characterization to identify the location and distribution of target antigens in suspension cells or in tissues by staining with a specific antibody. The antibody may be conjugated to either a fluorescent or an enzymatic label, and the location of the label seen through a microscope approximates the position of the target antigen. Here, immunohistochemistry and immunofluorescence for both paraffin-embedded and frozen tissues and for suspended cell are described. Moreover, specific recommendations for analysis of suspension of cells are provided.