Abstract: An implantable ultrafiltration device for removing low to medium molecular weight solutes and fluids from the blood of a patient experiencing renal failure, the device including: a pump having an inlet and an outlet; a first component for forming a first fluid flow path between the patient's vascular system and the pump inlet; a filter interposed in the first fluid flow path, the filter being permeable to water and substantially impermeable to blood cells and proteins; and a second component for forming a second fluid flow path between the pump outlet and the patient's bladder, wherein the pump, the first and second components, and the filter are all constructed to be surgically implanted in the patient's body.