The synthesis of liver collagen increases during the fibrotic process after administration of carbon tetrachloride and during regeneration after partial hepatectomy in rats. In the present study, we investigated the behavior of profilin and actin mRNA under such conditions. Profilin and actin mRNA increased after acute and chronic treatments of carbon tetrachloride, which is associated with the increase of fibronectin, type-III and -IV collagen mRNA. Furthermore, a simultaneous expression of profilin, actin and extracellular matrix proteins was observed during the regeneration of rat liver, that is, all mRNAs of these proteins showed biphasic peaks around 6 h and 48 h after partial hepatectomy. These results suggest that possible coupling might occur between the changes of extracellular matrix and the reorganization of actin cytoskeleton in vivo.