In 27 patients undergoing continuous pump-driven hemofiltration during intensive care, a new balancing device was used to control transmembrane pressure difference, and thus ultrafiltration rate, by means of an elastic reservoir and an infusion pump. The simultaneous infusion of substitution fluid by a second pump working independently of the former provided exactly and automatically the intended fluid balance. In only 0.7% of the total hemofiltration time (5519 h) could the preset ultrafiltration rate not be achieved. The simple components and installation of this device recommend its application in every intensive care unit that uses continuous arteriovenous or continuous pump-driven hemofiltration, relieving the staff and reducing unwanted and unnoticed deviations of intravascular volume and fluid balance.