Abstract: Blood purification apparatus comprises a dead-end system in which blood from the patient is allowed to flow through one or more purification modules, such as a dialyzer, a hemofilter, a hemoperfusion column and an oxygenator, into a resiliently walled reservoir, which is conveniently a standard blood bag. The direction of flow of the blood is then reversed by exertion of sufficient pressure on the bag to push the blood back through the purification module to the patient's circulation. Thus, since the reservoir is of available capacity, being of resilient material for example, the capacity of the apparatus remains equal to the volume of extra-corporeal blood.