Patients suffering from acute renal failure must undergo dialysis to substitute for the kidney's excretory function. Dialysis is a means of exchange between two solutions: blood and a liquid known as dialysate, across a semi-permeable membrane. This membrane permits the passage of water and aqueous solutions of low molecular weight but not that of the aqueous solutions of high molecular weight such as proteins. Dialysed patients are biologically monitored to prevent the various complications arising from blood dialysis, to check the efficacy of the treatment as well as to reduce the risk of morbidity and mortality. Because of the multiple and complex nature of renal functions, biological monitoring of a dialysis patients presents many, often inter-related facets. In addition to the complications inherent in dialysis itself, the dialysed patient is exposed to other causes of mortality or morbidity such as nutritional, hematologic, cardiovascular and infectious problems. Clinicians is confronted by other complications, albeit less common and easier to control, in the form of osteoarticular troubles or even aluminium poisoning. Lastly, biological assessment of the efficacy of purifying processing depends principally on calculating the dose of dialysate and the ureic index of subtraction which, in turn, requires the measurement of uremia.