An apparatus for performing haemodialysis on a patient, said apparatus comprising: - (i) a first blood transfer means for selectively withdrawing blood from a patient and temporarily storing it in a first storage portion, the first storage portion including a first orifice for the passage of blood into and out of said first storage portion; (ii) a filtration device through which the blood removed from the patient is passed in order to remove molecules from the blood; (iii) a second blood transfer means for selectively removing filtered blood from the filtration device and temporarily storing it in a second storage portion, the second storage portion having a second orifice for the passage of blood into and out of said second storage portion; whereby the first blood transfer means is additionally adapted to facilitate the transfer of blood stored in the first storage portion to the second storage portion via the filtration device, and the second blood transfer means is additionally adapted to facilitate the transfer of the blood stored in the second storage portion to the first storage portion via the filtration device, the apparatus further including a fluid measurement system (51a, 51b), which is configured to: - periodically measure the respective volumes of blood in the first and second storage portions; add the measured volume of blood in the first storage portion to the measured volume of blood in the second storage portion at that time, in order to calculate the total volume of blood within the first and second storage portions at that time; and compare the total measured volumes of blood within the first and second storage portions measured over a predetermined time interval to calculate the volume of fluid removed from the blood of the patient during that predetermined time interval, characterised in that: said transfer of blood between the first and second storage portions (5, 13) is through the first and second orifices; and in that the apparatus further comprises a valve mechanism arranged for selectively opening and closing a flow path between a patient access point and the first blood transfer means, and wherein the valve mechanism is configured such that when the flow path between the patient access point and the first blood transfer means is closed, a fluid path between the first blood transfer means and the filter is opened. (i) a first blood transfer means for selectively withdrawing blood from a patient and temporarily storing it in a first storage portion, the first storage portion including a first orifice for the passage of blood into and out of said first storage portion; (ii) a filtration device through which the blood removed from the patient is passed in order to remove molecules from the blood; (iii) a second blood transfer means for selectively removing filtered blood from the filtration device and temporarily storing it in a second storage portion, the second storage portion having a second orifice for the passage of blood into and out of said second storage portion; said transfer of blood between the first and second storage portions (5, 13) is through the first and second orifices; and in that the apparatus further comprises a valve mechanism arranged for selectively opening and closing a flow path between a patient access point and the first blood transfer means, and wherein the valve mechanism is configured such that when the flow path between the patient access point and the first blood transfer means is closed, a fluid path between the first blood transfer means and the filter is opened.