The effect of relaxin administration before (prevention) or after (treatment) the establishment of hepatic fibrosis in a mouse model was examined. In the prevention study, relaxin reduced collagen and smooth muscle actin content and significantly reduced serum levels of the liver enzymes alanine aminotransferase and aspartate aminotransferase. In the treatment study, administration of relaxin for 1 week reduced collagen and smooth muscle actin but not liver enzyme levels. Relaxin administered for 2 weeks had no significant effect. In conclusion, the data suggest that relaxin treatment before fibrosis can reduce collagen and improve liver function but that there is little effect of short-term relaxin treatment after fibrosis is established.