Improved survival of critically ill acute renal failure patients can be correlated with therapy dose. The overall solute elimination can be measured by the product of clearance and time (Kt), which is usually normalized for the volume of distribution (V) of the solute as “Kt/V.” Setting a Kt/V threshold of 1.4 can guide clinicians toward adequate treatment. This is a slightly higher prescription than the current value for chronic dialysis. However, the true uraemic toxins probably diffuse among body compartments less readily than urea and, as such, the frequency of renal replacement therapy should be more important to its efficiency, and should be optimal with continuous therapy. In the absence of an optimal dialysis dose, it can only be recommended that the prescription should exceed that calculated to be “adequate.”