[Modelling in hemodialysis. Why? How?]

It is an imperative necessity to adapt dialysis therapy patient to patient. This adaptation of dialysis procedure requires appropriate representation of water and solute exchanges. Kinetic modelling of hemodialysis was investigated in this respect. The goal of kinetic modelling is either to estimate one or several biologic parameters which are not easily measurable or to reach a prerequisite optimal physiologic state for a given patient. Constructing a model implies a physiological conception of solute and water exchanges that allows a definition of biologic parameters concerned. Mathematic equations only translate quantitatively water and solute transfers. A suitable model is in agreement with experimental data, and the best is the simplest. Therefore the capital point resides in the choice of assumptions which determine the model's precision and complexity. This review also outlined the limits of kinetic modelling which allows neither the determination of the best target nor the "a posteriori" justification of assumptions.