Although mitochondrial dysfunction is commonly accepted to mediate organ failure induced by systemic inflammatory response (SIR) the data on impairment of mitochondrial respiration upon SIR are still controversial. The aim of this study was to understand the contribution of mitochondrial reactive oxygen species (mtROS) to liver failure induced by SIR in rats challenged with lipopolysuccaride (LPS). A mitochondria targeted ROS scavenger, mitoTEMPO, did not influence drastic increase in cytokine levels (TNF, IL1, ect) peaking at first 4 hours in the blood of the rats, but it substantially attenuated organ damage (LDH, AST, ALT) occurring later at 16 h when the levels of pro-inflammatory cytokines dropped to normal values. As recently shown mtROS can activate NADPH oxidase of immune cells and damage host tissues if ROS are in excess. However, neither spontaneous nor PMA-induced ROS generations were influenced by mitoTEMPO in the total pool of immune cells, obtained from blood and lavages from peritoneum and lung; all three fluids predominantly contained neutrophils. In contrast, mitoTEMPO attenuated ROS produced by NOX in macrophages, which however did not contribute significantly to total ROS production in the body. Considering, that elevated mtROS levels in hepatocytes may cause their damage we incubated hepatocytes with cytokine mediators obtained by incubation of rat blood with LPS for 6, 12, and 24 hours. Inflammatory cytokines (IM) collected after 6 hours contained already all acute pro-inflammatory mediators (TNF, IL1, etc.) and they were able to up-regulate iNOS and IL6 in hepatocytes, but they did not increase mtROS production in the cells. IM collected at 12 and 24 h induced both expression of hepatocyte iNOS and IL6 and additionally mtROS generation; both gene expression and ROS generation were attenuated by mitoTEMPO. In conclusion, the acute phase cytokines released into the blood do not directly induce liver damage; there is another still undefined intermediate inducing liver damage in a mtROS dependent manner.