Abstract: A method and apparatus for extracorporeal circulation and treatment of blood. The apparatus comprises means for circulating and for treating blood, with a control system for controlling the circulating means. The circulating means includes tubing that directs blood to and from a microporous membrane. An arterial pump controls the flow rate of blood entering the filter; a venous pump controls the flow rate of blood exiting the filter. The filter includes a sealed, ported chamber surrounding the membrane. The rate of filtration of components removed from the blood through the membrane is directly proportional to a transmembrane pressure.Display and input devices transmit information between the central processor and an operator who operates the apparatus. The display and input devices include a keypad and an alphanumeric display. Sensors measure pressures within the tubing, at the inlet and outlet of the filter. Fluid flow rate can be calculated from the speeds of the pumps.