A simple and reproducible method is described for the measurement of mitogen-induced cytokine production in cultures of both human peripheral blood mononuclear cells (PBMC) and whole blood. In the culture supernatants the cytokines interleukin-1 alpha (IL-1 alpha), interleukin-2 (IL-2), interferon-gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) were determined by a rapid and sensitive immunoassay using various monoclonal and polyclonal antibodies. Comparing the PBMC cultures with the whole blood system a good correlation was obtained if the cell number was taken into account. In the post-induction supernatants the cytokine values were found to follow typical kinetic curves. The protocol was evaluated by screening 60 cancer patients with primary disease and 60 healthy controls. A markedly reduced secretion of IFN-gamma and IL-1 alpha was found in the cancer patients compared to controls, although leukocyte and lymphocyte counts were almost identical in both groups.