Several simple equations exist for Kt/V determination from pre dialysis (Cpre) and post dialysis (Cpost) blood urea. However, comparable equations have not been available for calculation of protein catabolic rate (PCR), an essential parameter for assessing patient status. Three simple formulas for PCR determination were developed from the urea mass balance equation for an anuric patient in protein steady state receiving thrice weekly dialysis. The simplest formula, PCR = 0.0076 [Kt/V] [Cpre + Cpost] + 0.17 relates PCR (in g protein/kg/day) to Kt/V and pre and post dialysis blood urea nitrogen measurements (in mg urea nitrogen/dl) for the midweek session. When tested for 540 simulated patients spanning a range of Kt/V (0.6-1.6); PCR (0.6-1.6 g/kg/day); dialysis duration t (2-4 hrs) and interdialytic weight gain expressed as a percentage of dry body weight gained daily (0-4%), this equation yielded a maximum error of less than +/- 5%, within the accuracy generally required for clinical needs. A more accurate formula, [formula: see text] where Clm is the logarithmic mean of Cpre and Cpost, gave maximum errors in PCR estimation for the same 540 simulated patients of less than +/- 0.6%. Both formulas require a precise value of Kt/V. The equation below incorporates a very accurate simple Kt/V equation recently published by the authors, allowing PCR to be expressed in terms of Cpre, the ratio of Cpost to Cpre (R), the ratio of session ultrafiltration volume (delta BW) to urea distribution volume (V), and dialysis time (t, in min). [formula: see text] This equation was accurate to within a maximum error of +/- 1% for the simulated patient group. These equations allow simple and accurate patient PCR determination, and should be used in conjunction with a simple formula for accurate Kt/V determination to guide end-stage renal failure patient therapy.