A method for priming a hemodialysis treatment includes: providing a disposable cassette including at least a portion of a dialysate circuit and at least a portion of a blood circuit; placing a dialyzer in fluid communication with the dialysate circuit via a to-dialyzer dialysate line and a from-dialyzer dialysate line; placing the dialyzer in fluid communication with the blood circuit via an arterial blood line and a venous blood line; placing a source of dialysis fluid in fluid communication with the dialyzer; priming the dialysate circuit with dialysis fluid from the source while both the to-dialyzer dialysate line and the from-dialyzer dialysate line are connected at their dialyzer ends to the dialyzer; and priming the blood circuit with dialysis fluid from the source by actuating at least one valve provided by the disposable cassette.