An in vitro assay for the detection and enumeration of mouse and human cytokine-secreting cells is described and some ways in which it may be used diagnostically are indicated. The assay is an extension of the ELISA plaque assay or ELISPOT assay and uses pairs of antibodies to capture and then visually develop secreted lymphokines. In this way, it is possible to enumerate the specific cytokine-secreting cells. This assay may provide a valuable tool in the clinical investigation of the mechanisms of disease development and tissue destruction.