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The functional capability to produce interleukin 2 (IL2) and interferon gamma (IFNγ) by peripheral blood lymphocytes (PBL) from elderly humans was evaluated. Thirty-nine samples of PBL derived from donors aged from 56 to 79 yr were cultured with phytohaemagglutinin (PHA) as stimulus at 37°C for 48 hours. The IL2 activity in the supernatants was measured by its ability to sustain the IL2-dependent CTLL growth. Cultures of elder human T cells produced low level of IL2 activity, that is on the average of 9.7±9.8 μ/ml, equivalent to 28.1% the IL2 activity in parallel cultures of PBL derived from young donors (34.2±8.3 μ/ml, assessed on the basis of 145 samples). In the elder humans, the IL2 production by PBL decreased progressively as the increase of the age of the donors.In contrast to the impairment of IL2 production, the amount of IFNγ secretion by elder human T cells was almost at the same level as that by young human T cells. The average IFNγ activity of 39 samples of elder PBL cultures and 128 samples of young PBL cultures was 2,961±736 μ/ml and 3133±950 μ/ml, respectively.There was no significantly positive correlation between the level of IL2 and IFNγ when comparison was made based on each individual samples. This implies that it may exist an alternative way of IFNγ production which does not require the induction by IL2, and the relatively high level of IFNγ may not impose adverse effect on the IL2 production.