A technique for intracytoplasmic immunofluorescence staining to detect and quantify human interleukin-1 alpha (IL-1 alpha) and beta (IL-1 beta) in CD4, CD8, and CD14 positive lymphoid cells is described. Mononuclear cells stimulated in vitro with PHA to produce IL-1, were fixed and made permeable to antibodies by sequential exposure to paraformaldehyde and the detergent n-octyl-glucoside. Cytoplasmic and surface staining of both forms of IL-1 were demonstrated by indirect fluorescence using IL-1 beta and IL-1 alpha specific mouse monoclonal antibodies and quantified with flow cytometry.