The intracellular accumulation of five different lymphokines in individual cells could be identified by lymphokine-specific antibodies and an indirect immunofluorescence technique with UV microscopy. When peripheral blood mononuclear cells from one healthy donor were activated in vitro by the T cell mitogen anti-CD3 monoclonal antibody, the maximal number of cells producing interleukin (IL)2, IL 6 or tumor necrosis factor (TNF)-alpha occurred 6 h after initiation of the cultures, while peak numbers of interferon-gamma, TNF-beta and a second wave of TNF-alpha-synthesizing cells were noted approximately 20 h later. By performing two-color immunofluorescence studies we observed a variegated production pattern with cells making no, one or several lymphokines simultaneously. All five cytokines accumulated in the Golgi organelle resulting in a very characteristic morphology of the staining with or without additional cytoplasmic immunofluorescence.