We have investigated the effect of age and of the presence of proinflammatory cytokines on Hsp 70 production in human peripheral blood mononuclear cells, using flow cytometry. Twenty-seven women and 23 men, all apparently healthy, participated in the study. At 37 degrees C, the percentage of Hsp 70-producing monocytes and lymphocytes, as well as the level of Hsp 70 in monocytes, were negatively influenced by age. After exposure of the cells to 42 degrees C, the increase of Hsp 70 production was more pronounced in monocytes than in lymphocytes; both the intensity of Hsp 70 production and the percentage of Hsp 70-producing cells were negatively influenced by the age of the subjects, as well for monocytes as for lymphocytes. There was a negative correlation between the intensity of Hsp 70 production by monocytes exposed to 42 degrees C and the serum levels of tumor necrosis factor-alpha and interleukin-6. In conclusion, in human monocytes and lymphocytes, heat-induced Hsp 70 production is reduced with increasing age and is negatively influenced in monocytes by proinflammatory cytokines.