The assessment of the level of hydration in the intravascular fluid compartment in acute renal failure (ARF) and multiple organ failure (MOF) is of an utmost importance. However, the data on monitoring of blood volume in these diseases and especially during haemodialysis treatment are lacking. This article summarizing the experience of monitoring of blood volume in chronic haemodialysis suggests that the application of such monitoring will contribute to better results in haemodialysis treatment of ARF and MOF.