Mn(III)tetrakis(N-ethylpyridinium-2-yl)porphyrin, MnTE-2-PyP 5+ , a potent catalytic superoxide and peroxynitrite scavenger, has been beneficial in several oxidative stress-related disease thus far examined. Pharmacokinetic studies are essential for the better assessment of the therapeutic potential of MnTE-2-PyP 5+ and similar compounds, as well as for the modulation of their bioavailability and toxicity. Despite high hydrophilicity, this drug entered mitochondria after single 10 mg/kg intraperitoneal injection at levels high enough (5.1 µM; 2.95 ng/mg protein) to protect it against superoxide/peroxynitrite damage. Utilizing the same analytical approach, which involves the reduction of MnTE-2-PyP 5+ , followed by the exchange of Mn 2+ with Zn 2+ , and HPLC/fluorescence detection of ZnTE-2-PyP 4+ , we measured levels of MnTE-2-PyP 5+ in mouse plasma, liver, kidney, lung, heart, spleen, and brain over a period of 7 days after a single intraperitoneal injection of 10 mg/ kg. Two B6C3F1 female mice per time point were used. The pharmacokinetic profile in plasma and organs was complex; thus a non-compartmental approach was utilized to calculate the area under the curve (AUC), c max , t max , and drug elimination half-time (t 1/2 ). In terms of levels of MnTE-2-PyP 5+ found, the organs can be classified into 3 distinct groups: (1) high levels: kidney, liver, and spleen; (2) moderate levels: lung and heart; and (3) low levels: brain. The maximal levels in plasma, kidney, spleen, lung, and heart are reached within first 45 minutes whereas in case of liver a prolonged absorption phase was observed with the maximal concentration reached at 8 hours. Moreover, accumulation of the drug in brain continues beyond time of the experiment (7 days) and is likely driven by the presence of negatively charged phospholipids. For tissues other than brain, a slow elimination phase (single exponential decay, t 1/2 = 60 to 135 hours) is observed. The calculated pharmacokinetic parameters will be used to design optimal dosing regimens in future preclinical studies utilizing this and similar compounds.