Previously we studied levels of the cytokine IL-6 and activation of the complement and contact system and of neutrophils in a group of 48 patients with sepsis. Some of these inflammatory parameters appeared to be associated with a poor prognosis. Here we report on the relationships of C4a and C3a (complement activation products), of factor XII and prekallikrein (contact system proteins), of elastase (a protease released by activated neutrophils) and of the cytokine IL-6 to hemodynamic and biochemical parameters measured in those 48 patients at the time of admission to the Intensive Care Unit. No significant correlations between any inflammatory parameter and either systemic vascular resistance or cardiac index were found. Mean arterial pressure significantly correlated with both factor XII and prekallikrein levels. Lactate correlated with C3a and C4a, with elastase, and in particular, with IL-6, whereas it did not correlate with either factor XII or prekallikrein. Platelet numbers inversely correlated with both C3a and C4a, as well as with elastase and IL-6, whereas they positively correlated with factor XII and prekallikrein. Based on these findings we propose a model for the interplay of these inflammatory mediators in the pathogenesis of sepsis. This model takes into consideration the occurrence of capillary leakage, shock, disseminated intravascular coagulation, thrombocytopenia and of acute phase reactions in sepsis.