A single needle hemo(dia)filtration apparatus comprises a blood treatment membrane device, a first pump that continuously circulates fluid in a closed annular portion of an extracorporeal blood circuit, means for continuously performing ultrafiltration through the membrane, and a second pump that infuses a substitution fluid flow rate into the extracorporeal blood circuit that is less than the ultrafiltration flow rate in an arterial phase of withdrawal from the patient and that exceeds the ultrafiltration flow rate in a venous phase of restitution to the patient.
