Adult respiratory distress syndrome (ARDS), a multifactorial disease with poor prognosis, is characterized by an accumulation of inflammatory cells within the airspaces of the lungs. There is evidence that alveolar macrophages (AM) are involved in the pathogenesis of this pulmonary disease. It has been demonstrated that AM synthesize heat shock proteins (HSPs) after exposure to certain stress factors. Increasing evidence suggests that HSPs could confer protection against oxidative injury, noxious molecules, and bacterial toxins. In stressed cells HSP 72 appears to be essential for survival during and after exposure to cellular injury. The aim of this study was to evaluate the magnitude of HSP 72 expression by human AM of patients with ARDS and correlate that with respiratory burst activity. Bronchoalveolar lavage was performed in six ARDS patients, 10 patients with high risk for developing ARDS, and two patients who underwent bronchoscopy for other reasons. Spontaneous ex vivo expression of HSP 72 in AM could be demonstrated by immunocytochemistry. Total RNA as well as poly(A)-rich mRNA were extracted from recovered AM and analyzed by Northern blot and slot blot using a human HSP 72-specific probe. Signals of slot blot were analyzed by densitometry and expressed as relative levels of HSP 72 mRNA of stressed (42 degrees C) HT 1080 control cells. Significantly (p < .001) higher levels of HSP 72 mRNA were measured in patients with ARDS (96.2 +/- 9.5 relative levels) in comparison to those not developing this syndrome (46.0 +/- 4.2). With regard to respiratory burst activity of AM in patients with ARDS, there was a negative correlation between HSP 72 expression and reactive oxygen species production. The AM of patients with ARDS with high relative levels of HSP 72 expression showed low respiratory burst activity. A predictive value for disease severity of high level of HSP 72 mRNA in AM in patients at risk for ARDS has to be evaluated by future studies. This demonstration of HSP 72 expression ex vivo suggests a protective role of HSP response against endo/exogenously generated stress factors in AM.