This paper describes a technique for increasing the ultrafiltration flux from blood in hemofiltration used for the treatment of end-stage renal failure. This technique is based on the principle that the filter transient response to a step change in transmembrane pressure Delta P-step from an unpolarized state to a highly polarized state can temporarily exceed the maximum UF flux J(fp), at plateau, reached in a stationary regime. We have demonstrated that the total filtrated volume can be appreciably improved by applying periodic stepped pressure increments and by appropriately choosing the kinetic parameters tau(1) duration of high-pressure phase (>80 kPa) and tau(2) duration of low-pressure phase (<10 kPa). This improvement occurs only if a backwash flow Q(ret) around 3 cm(3)/s is applied to the filter during t(2) in order to depolarize the membrane, and if tau(1) and tau(2) are close to 20 and 2 seconds, respectively, when the inlet flow Q(i) is chosen in the range from 1.7 to 5.0 cm(3)/s for a membrane area of 0.65 m(2). The relative gain G between the total filtrated volume obtained in a dynamic regime and the one obtained in a stationary regime can reach 60%. We have found that G mainly depends on Delta P-step and tau(1). This technique has been shown not to hemolyze the blood and to retain its efficiency over long periods.