Nineteen controls, six SIRS patients and 25 severe sepsis patients were studied. The percent expression of HLADR on CD14+ monocytes was significantly different between the three groups showing progressive decrease from controls (mean 90.5 ± 3.8%) to SIRS (mean 61.2 ± 5.9%) to severe sepsis (mean 39.2 ± 5.5%) patients (controls vs. severe sepsis, P < 0.001; controls vs. SIRS, P = 0.006; SIRS vs. severe sepsis, P = 0.03). hsp70 and hsp90 MFIwere significantly different between controls (mean 49.5 ± 4.9 and 33.5 ± 3.4 respectively), SIRS (mean 69.9 ± 16.5 and 46.5 ± 5.7 respectively) and severe sepsis patients (mean 33.3 ± 4.5 and 21.7 ± 2.7 respectively) (P < 0.05 for all comparisons). Notably, the hsp level rose from controls to SIRS and fell from SIRS to severe sepsis patients. APACHE score increased significantly (P = 0.023) in septic patients compared with SIRS.