Ischemia reperfusion injury (IRI) is a problem in organ transplantation. Relaxin is known to have a protective effect against liver injury caused by IRI. Using a model of isolated perfused rat liver, the local oxygen supply in liver tissue was investigated by spectrophotometric in vivo imaging and compared to the protective effect of relaxin shown by immunohistochemical measurement of myeloperoxidase and malonyldialdehyde activities as determinants of oxidative stress. In relaxin-treated liver tissue, spectrophotometry showed a better oxygen supply and decreased myeloperoxidase and malonyldialdehyde activities. Our data suggest that relaxin can influence the oxygen distribution in liver tissue and reduce cell damage caused by IRI.