It is well known that ageing is associated with various alterations of the lymphoid cell functions. Although both B and T cell are affected, the last appear to be more sensitive to ageing process. During the past years, to gain insight into thé mechanism(s) of this impairment, effort has been centered on the helper T cells specifically engaged in the production of interleukin-2 (IL-2) because of the pivotal role played by this cytokine in the activation of several immune functions. The results have demonstrated that the ability to produce IL-2 declines with age. In this paper we report the results of a study performed to determine the influence of age on the capacity to produce gamma-interferon (gamma-IFN), interleukin-4 (IL-4) and interleukin-6 (IL-6). Mononuclear cells from young and old subjects were assessed for cytokine producing capacity in response to phytohaemagglutinin stimulation. A significant decrease of gamma-IFN production by old subjects has been observed. No significant difference was instead observed between the old subjects and the young ones as regards IL-4 and IL-6 production. We suggest that this imbalanced cytokine production may well account for the pattern of immune response which may be observed in elderly, i.e. a normal or increased humoral response in face of a low T cell immune responsiveness.