The traditional control of the dialysis session comes about by means of an open-loop system. At the beginning of the session some parameters are set, such as the kind of dialyzer, the blood flow, the ultrafiltration rate, the dialysate conductivity and the dialysate temperature. Generally speaking, these parameters are not modified unless there occur complications in the patient that call for adjustments to be made. The biofeedback concept, which is synonymous with a closed-loop control of biological variables, presupposes, on the other hand: the continuous measurement of a variable thanks to a specific sensor its evaluation by a sort of expert system--the so-called controller and a series of means--the actuators--that allow the behavior of the variable to be directly or indirectly influenced. In clinical practice, different biofeedback systems are emerging, addressed to the control of blood volume, body temperature, and blood pressure. Each one of these systems has been successfully deployed, especially in the management of "difficult" patients unstable from the hemodynamic point of view. However, the future will be an integrated system that sees a complex adaptive, multi-input, multi-output controller which, with a great simplicity of use and low costs, will allow renal replacement therapy to be increasingly physiological and more efficient.