BACKGROUND Lipid peroxidation processes (LPO) are evident in many organ failures. Due to their toxic properties, they are causative for cellular dysfunction at the site of their origin and far beyond. This study was conducted to investigate differences in LPO pattern of patients with established acute respiratory distress syndrome (ARDS) and patients with end-stage liver failure undergoing liver transplantation (LTX) as two mayor prototypes of organ failure. METHODS In this prospective, nonrandomized, controlled trial, we examined LPO by measuring malondialdehyde (MDA), and the volatile aldehydes hexanal and propanal as LPO-markers. Eighteen patients with ARDS, 16 subjects undergoing liver transplantation due to liver failure, and 8 healthy controls were included to the study. RESULTS ARDS patients showed significantly higher levels in MDA concentrations than LTX and controls, respectively. However, MDA levels of patients with end-stage liver failure were equal to those of controls. Blood concentrations of hexanal and propanal, specific by-products of lipid peroxidation, were elevated in both patient groups, but significantly higher only in LTX. Unexpectedly, hexanal and propanal concentrations were significantly higher in LTX than in ARDS patients. In both patient groups, MDA showed no differences between arterial and mixed venous blood, whereas volatile aldehydes were higher in arterial than in mixed venous compartment. CONCLUSIONS Both ARDS and LTX-patients showed significant evidence of enhanced LPO. However, proportions of MDA and volatile aldehydes differed substantially between the groups. Thus, for the interpretation of LPO markers, disease-specific factors have to be taken into account. Distinctions might be attributable to differences in the effected lipid components or variations in metabolism.