This study investigates heat shock protein 70 (HSP70) expression by peripheral blood mononuclear cells (PBMCs) of septic patients admitted to an intensive care unit and examines the possibility of a correlation between HSP70 levels and plasma tumor necrosis factor alpha (TNF-alpha) concentrations. Additionally, we evaluated whether the HSP70 production could be regarded as a prognostic factor for the development of septic shock as well as for patient survival. Blood samples of 29 patients were taken 24 hours after the diagnosis of sepsis. HSP70 expression and TNF-alpha level were measured using indirect immunofluorescent analysis and a commercially available enzyme-linked immunosorbent assay method, respectively. PBMCs expressed significantly high levels of HSP70 (11.9 +/- 5.6 [sd]) compared with those of the healthy control group (3.2 +/- 2.1% positive cells). Such enhanced levels were correlated to plasma TNF-alpha concentrations (r = .99, P < .01). This study failed to demonstrate a relationship between HSP70 production and clinical outcome. These findings give further evidence that also in humans, heat shock response is activated during sepsis. The correlation observed between HSP70 overproduction and TNF-alpha plasma concentrations suggests that HSP70 exerts a possible protective effect against TNF-alpha cytotoxicity. Such hypothesis has not been confirmed by our clinical data.