Subepithelial fibroblasts which form cellular network beneath the epithelium of rat intestinal villi were cultured, and their structure and function were examined. Cultured subepithelial fibro-blasts, each resembling a maple leaf, were rich in bundles of microfilaments, synthesized collagen fibrils, and were connected each other with a few small gap junctions. By the treatment of dBcAMP, the flat cells changed their morphology to a stellate form with several thin processes within 1hr. This morphological conversion was reversible and also occurred with folskolin or cholera toxin treatments. By the addition of endothelin-1 or -3, stellate cells reassumed a flat morphology within several minutes. Endothelin induced a transient increase and sometimes following oscillations of intracellular Ca^<2+>, where the initial phase of intracellular Ca^<2+> increase was due to the release from intracellular store and the second phase was owing to the Ca^<2+> influx. However, the intracellular Ca^<2+> increase was not necessary for the morphological conversion, because BAPTA-am treated cells diminished Ca^<2+> response but persisted the morphological change. The morphological conversions were considered to depend on the concentration of intracellular cAMP but not on Ca^<2+>. Subepithelial fibroblasts also have receptors of serotonin, substance P, angiotensin II. These properties of subepithelial fibroblasts were similar to those of astrocytes. These results indicate that subepithelial fibroblasts of small intestine have similar morphological and functional properties with astrocytes.