A theoretical model of the vascular network of normal rabbit small intestine mucosa was constructed from tissues injected with silicone latex. The segmental resistances of the network were calculated from Poiseuille's law by use of lengths and radii measured microscopically and a value of 0.03 P for the viscosity of blood. Where required for the theoretical calculations, published values were used for pressures in arteries down to 20 micrometer in diameter. Values for total-organ blood flow, its distribution between mucosa and nonmucosa, and the partition of mucosal flow between crypts and villi were similar to values measured in the same animals with microspheres. Blood pressures in arteries smaller than 20 micrometer in diameter were also similar to published values. Mean mucosal capillary pressures were close to published experimental estimations. The model seems to provide a useful starting point for describing the magnitudes and patterns of pressures and flow in the small intestine and for consideration of specific location of the sites of their control.