There is a striking correlation between nitric oxide (NO) production and myeloper-oxidase (MPO) enzyme activity accession in various tissues after endotoxemia. Both arginine-NO and arginine-asymmetric dimethylarginine (ADMA) pathways have been recognized to play critical roles during infection and inflammation. We investigated whether there is a link between MPO-mediated nitrating pathway and arginine-ADMA pathway after endotoxemia in liver. All experiments were performed in two groups (control and endotoxemia) of 10 guinea pigs. In this study, 6 h after the administration of endotoxin at a dose of 4 mg/kg, MPO activity and ADMA, L-arginine, and 3-nitrotyrosine (3-NT, a stable product of peroxynitrite formation) levels were measured. Measurement of ADMA and L-arginine were accomplished by HPLC with fluorescent detector. 3-NT was quantified by HPLC with electrochemical detector. MPO activity was determined by spectrophotometric method. After administration of endotoxin, ADMA and L-arginine levels decreased, but 3-NT levels and MPO activity increased significantly. In conclusion, there is an inverse relationship between MPO-mediated tyrosine nitration and arginine-ADMA pathway in liver after endotoxemia.