T he retractile and remodeling phenomena accompanying and, in pathologic situations, following the healing of an open wound have attracted the interest of physicians and scientists for many centuries. It has long been assumed that these phenomena depend on extracellular matrix reorganization; however, the demonstration that fibroblastic cells acquire contractile features during the evolution of granulation tissue (for review, see Schürch et al, 1998) has switched the interest from the extracellular to the intracellular compartment. The past 30 years have seen the accumulation of advances in the field of contractile fibroblasts or myofibroblasts that presently appear to be the key cell for the production of granulation tissue remodeling. Myofibroblasts are obviously also producing extracellular matrix components such as collagen and fibronectin, and it has become clearer that granulation tissue remodeling depends on the coordinate activities of intracellular and extracellular molecules. The interactions of these molecules are under the control of microenvironmental factors such as transforming growth factor-(TGF-) or other cytokines and mechanical stress. The purpose of our review is to summarize recent advances made in this field by several laboratories, with special emphasis on the evolution of fibrotic phenomena in the liver and the kidney.