Up to the present, ten models have been proposed or applied to analyze the relationship between blood flow and intestinal absorption. The conceptions of these models and their basic and final equations are described. In addition, their relationship to the first-order rate constants used in the models not explicitly including the blood flow rate is elucidated. Usually a curvilinear (concave curvature) relationship between the blood flow rate and the absorption rate is predicted by the models. This similarity of the curves is the reason that in many cases several models are compatible with the experimental data.