Mild forms of intestinal epithelial injury commonly occur in many disease states. In order to study how such epithelial" wounds" heal, we have developed a highly reproducible in vitro model of intestinal epithelial injury. Guinea pig ileal mucosal sheets were mounted in Ussing chambers and the mucosal surfaces were exposed to 0.06% Triton-X 100 for 5 minutes. This resulted in denudation of the epithelium at the tips of 86% of villi. As a result of this injury, resistance to passive ion flow decreased significantly (56.5+/-1.3 versus 38.4+/-2.3 ohm. cm2 for control and injury, respectively, p less than 0.01), as did transepithelial potential difference (-11.9+/-0.7 versus-4.3+/-0.4 mV for control versus injury respectively, p less than 0.01). In parallel, transepithelial fluxes of the extracellular space markers mannitol and inulin increased 3-to 5-fold immediately after injury. Two hours after injury, villus tips were again confluently covered by columnar absorptive cells, a time course of healing too fast to be accounted for by enhanced cell proliferation. Analysis of the structural events occurring during recovery showed that absorptive cells shouldering the foci of denudation rapidly changed shape after injury: they became flattened and sent cell projections over the denuded basement membrane. By 60 minutes after injury, cells from opposite shoulders of the denudation abutted, thus resealing the defect. Paralleling these structural changes, transepithelial resistance, potential difference, and mannitol and inulin fluxes returned toward control values. These data show that focal epithelial discontinuities in the small intestine may be rapidly resealed. Such reparative processes may substantially limit the deleterious physiologic impact of superficial forms of intestinal injury.