A dialysis system operates to supply dialysate to a dialyzer from a feed chamber in response to a reduction in the volume of the feed chamber, and to recover used dialysate which is flowed out from the dialyzer into a recovery chamber in response to an increase in the volume of the recovery chamber. The increase in the volume of the recovery chamber is greater in magnitude than the magnitude of a reduction in the volume of the feed chamber, with a difference therebetween being effective to control the amount of ultrafiltration. At least two sets of feed chambers and recovery chambers may be provided, and a supply of the dialysate from the other feed chamber may be initiated before the supply from one of the feed chambers is completed, thus allowing the dialysate to be continuously supplied to the dialyzer.
