AbstractThe principal technique described in this unit was developed for detecting cytokines produced by T cells, specifically interferon gamma (IFN‐γ) and interleukin 4 (IL‐4). In addition to providing information about which cytokines are being produced, it also helps to phenotypically identify the specific cells producing them. For example, CD4+ or CD8+ cells can be subdivided into TH1/TH2 helper cells or TC1/TC2 suppressor cells, respectively. This procedure can be useful in examining the response of cells to a variety of agonists, the immune function in various disease states, and the level of lymphocyte activation or suppression. In addition, it can be used to detect a variety of cytokines in many cell types, although the methodology must be carefully evaluated for each cytokine or cell type of interest. Additional methods are included for the stimulation of T cells with allogeneic cells and for the performance of controls for labeling specificity.