Myeloperoxidase (MPO), which is exclusively contained in neutrophils, is released on their activation. Therefore, MPO may possibly be used as a parameter of neutrophil activation. Thiobarbituric acid-reactive material (TBARM) reflects lipid peroxidation and is a parameter of oxygen radical-mediated cell membrane damage. Using our guinea pig model of septic lung injury we measured MPO and TBARM in the setting of acute lung injury. The two experimental groups were saline controls (n = 8) and an E. coli septic group to which 2 x 10(9) live E. coli were administered intravenously (n = 8). Lung damage was assessed by measuring wet to dry lung weight ratio (W/D) and lung tissue to plasma accumulation of 125I-albumin (AL: albumin leakage). We measured MPO and TBARM in plasma and BAL fluid. Increased W/D and AL were observed in the E. coli group suggesting the development of acute lung injury. In the E. coli group, plasma MPO increased and MPO in BAL fluid was significantly increased as compared with the saline control group. There was no difference in plasma TBARM between the two groups, while TBARM in BAL fluid of the E. coli group was greater than in that of controls. Although BAL fluid TBARM correlated with both W/D and AL, there was no relation between BAL fluid MPO and either of these parameters. We conclude that TBARM in BAL fluid may be useful for assessing E. coli-induced acute lung injury in guinea pigs.