The midgut epithelium of larval Lepidoptera consists of a monolayer of mature columnar and goblet cellsin vivowith loosely bound stem cells at its base. Cultures ofHeliothis virescensmidgut contained quiescent and dividing stem cells, differentiating and mature cells as well as small rows of attached cells, randomly distributed in the culture vessel. Fixed cultures were immunostained with polyclonal antibodies to fibronectin and integrin β1. Many stem cells stained darkly; lighter staining stem cells imply that some stem cells can become less adhesive. Developing cells were pale, lacking integrin and fibronectin epitopes on their surfaces, and were probably poorly adhesive. During a moltin vivo, differentiating stem cells insert between existing epithelial cells, increasing gut size; lack of stickiness would enable them to do so. As pre-columnar cells differentiatedin vitro, stainability reappeared. Mature columnar cells were decorated with a pattern of intense surface immunostaining material. Small immature columnar and goblet cells adhered to the distal ends of mature columnar cells by their proximal areas near a fibronectin positive area. Goblet cells, seldom found togetherin vivoorin vitro, lacked prominent fibronectin or integrin-like surface proteins. Cells were joined to each other in the same orientation and cell pattern observed in intact midguts. The pattern was achievedin vitroby cell-cell adhesion without basal membrane or existing midgut as guides.