Abstract: A peritoneal dialysis apparatus comprising a plurality of components including a catheter, a fluid heater, a fluid weighing means and a control device. The components are interconnected by conduits so that fluid can flow from the heater to the peritoneal cavity by way of the catheter, and then from the peritoneal cavity to the weighing means. The weighing means measures the quantity of discharged fluid as a result of the introduction of the dialysis fluid to check that the dialysis fluid is causing fluid to drain from the peritoneal cavity. The flow of fluid between the components of the system is controlled by valves which are selectively opened and closed.