The aim of the present study was to investigate the in vitro mitotic response and cytokine production after allogeneic stimulation of peripheral blood mononuclear cells (PBMC) from healthy elderly subjects. Interleukin-1 (IL-1), interleukin-2 (IL-2), gamma-Interferon (gamma-IFN), and Tumor Necrosis Factor alpha (TNF-alpha) were detected in the supernatants of mixed lymphocyte cultures (MLC). The in vitro proliferative response was significantly reduced in the elderly subjects. The amount of IL-2 detected in the supernatant from cultures of cells from elderly donors was higher than for young controls, as were the production of cytokines predominantly secreted by the macrophage population (IL-1 and TNF-alpha). There was no difference in the production of gamma-IFN by cells of elderly and young subjects.