We describe a flow cytometry method to simultaneously analyze IFN-gamma production and T cell surface phenotype in freshly isolated lymphocytes without requiring prior in vitro stimulation. We show that enumeration of intracytoplasmic IFN-gamma positive T cells correlates with quantitative measurement of IFN-gamma in culture supernatant fluids. This suggests that cytokines can be reliably measured using flow cytometry. Flow cytometry has the added advantage of simultaneous detection of cell surface markers. Furthermore, we suggest that analysis of ex vivo IFN-gamma production at the single cell level may reflect more accurately T cell IFN-gamma production, by avoiding the polyclonal stimulation of IFN-gamma production observed after short term in vitro stimulation.