We have used a multiplex bead array assay to detect simultaneously 25 different circulating cytokines in 35 control subjects (young versus old) and 29 patients (young versus old) with acute infection. Intracellular PBMC levels of heat shock proteins (Hsp) were determined using flow cytometry. Levels of MIG and IL-6 were higher in the elderly normal subjects and patients, respectively, compared to their young counterparts. Hsp32, Hsp70 and Hsp90 were higher in elderly compared to young normal subjects. This difference disappeared for patients with inflammation who had increased levels of Hsp32, Hsp70 and Hsp90 compared to normal subjects. Most striking, a different pattern of association between cytokines and Hsp was noticed in healthy elderly subjects compared to the other groups of participants. It is concluded that age-related stress, possibly oxidative, which can down-regulate cytokine production with a concomitant up-regulation of Hsp production, could be involved in this differential pattern of association.