Peripheral blood mononuclear cells were cultured for 72 hours in presence of phytohaemagglutinin (PHA), phytohaemagglutinin/phorbolmyristate acetate (PHA/PMA), pokeweed mitogen (PWM) and in absence of these stimulators. The IL-2 concentrations of cultural supernatants were determined by an IL-2 dependent cell line. There was no IL-2 determined in absence of any mitogenic stimulators. Induction of IL-2 by PWM does not require the presence of PMA in contrast to stimulation by PHA/PMA, where PMA was found to be necessary for stimulation of production of IL-2. PHA/PMA induced IL-2 release shows only a weak maximum at 24 hours, whereas PWM induced IL-2 release was found to have a clear maximum at 48 hours. Stimulation by PWM enables comparative examination of DNA synthesis (lymphocyte transformation test) and IL-2 production in the same cell system using only one mitogen.