Abstract: Dialysis systems that remove air from a blood circuit are disclosed herein. In an embodiment, a dialysis system includes a dialysis fluid circuit, a blood circuit including an arterial line, a venous line, and an enclosure in fluid communication with the venous line, the enclosure configured to release air through a hydrophobic vent for priming the blood circuit, a blood pump configured to pump fluid through at least the arterial line, a first valve operable with the arterial line and a second valve operable with the venous line, and a pumping and valving algorithm operated after priming to remove air from the blood circuit to control the first and second valves and the blood pump to replace priming fluid with blood from a patient.