Autologous gut smooth muscle graft of two piglets was used for creating a ring in sigmoidostomy. The graft was investigated several times by histology and electron microscopy. A sort of myofibroblasts were observed the 7th day in the smooth muscle. Three months later the smooth muscle was completely transformed into a cellular connective tissue comprising myofibroblasts and fibroblasts. The experiment points to possible relation of smooth muscle cell, myofibroblast and fibroblast.