The three-dimensional organization and ultrastructure of lymphatics in the rat intestinal mucosa were studied by scanning electron microscopy using the KOH-collagenase digestion method (to remove extracellular connective tissue matrices) and by conventional transmission electron microscopy. Each villus possessed three or more lymphatics in the deeper layer of the lamina propria. These initial lymphatics were 5-15 microns in diameter and ran parallel to each other in the longitudinal direction of the villus. These lymphatics were free from adhering periendothelial cells, but had numerous cytoplasmic folds and projections of the endothelium on their abluminal surface. At the villous base, the lymphatics emptied into several thicker (about 70-80 microns) lymphatics, which further connected together to form a flat and wide sinus (intra-villous lymphatic sinus). This sinus was relatively smooth in abluminal surface. From the bottom of each sinus, several lymphatics descended perpendicularly to drain into lymphatics in the submucosa. The villous lymphatics described above seemed to be partially accompanied by bundles of smooth muscle cells, which ran longitudinally in the villous core. The submucosal lymphatics were smooth in abluminal surface and possessed no periendothelial cells. These lymphatics ran in a transverse direction just beneath the muscularis mucosae to form a two-dimensional mesh-work by anastomosing with one another. This submucosal lymphatic network was often closely associated with the muscle cells of the muscularis mucosae, but was not accompanied by submucosal arteries.