Sepsis may initiate acute respiratory distress syndrome which may be accompanied by an increased pulmonary epithelial-endothelial permeability. In this study, sepsis was induced by an intraperitoneal implantation of gelatine capsules containing Escherichia coli/Bacteroides fragilis adjuvant substance. The importance of bacteria in sepsis-related lung injury was studied in rats given an intraperitoneal injection of E. coli or in rats given the adjuvant substance alone in capsules intraperitoneally. Rats with empty capsules were used as controls. The rats were intratracheally instilled with bovine serum albumin (BSA) directly after the capsule implantation or the injection of E. coli, and the passage over the lower respiratory tract was assessed as blood plasma levels of immunoreactive BSA. The plasma BSA levels in the control rats increased continuously up to 24 h after intratracheal instillation. This increase was significantly augmented already 1 h after the septic challenge, i.e. before any clinical symptoms were observed, in both the septic rats and the rats with the E. coli injected intraperitoneally. Furthermore, the time required to obtain maximal plasma BSA levels was shorter in septic, adjuvant-exposed and in E. coli-injected rats than in the controls. The plasma levels and the total BSA passage over the lower respiratory tract was significantly higher (p < 0.001) in the septic and in the E. coli’-injected rats than in the adjuvant-exposed and the control rats. The results indicate that macromolecules pass over the lower respiratory tract into the blood circulation in higher amounts in septic than in control rats and rats exposed only to adjuvant substance already before any clinical signs of sepsis are observed, and that this effect may be due to bacteria and/or bacterial products. This increased inward passage may reflect the early damage to the epithelial-endothelial barrier of the respiratory tract in sepsi