From both human and animal tissues, myofibroblasts can be successfully cultured in vitro through multiple passages. As compared with cultured fibroblasts from control tissues, early passage myofibroblasts have slower growth cycles, as is typical of highly differentiated cells. Also in early passage, differences between myofibroblasts and fibroblasts in tissue culture in vivo can be preserved. Late passage animal studies suggest dedifferentiation in both morphology and growth cycle rate. As indicated by our data, which have been discussed in detail in our previous investigations, we believe that further studies may help to define how such dedifferentiation occurs and may determine ways to do so clinically. However, such control attempts must take into account the heterogeneity of myofibroblast and fibroblast populations which these studies have identified.