Urea kinetic analysis allows for the calculation of the urea distribution volume and urea generation rate. This method was employed in patients with acute renal failure managed by continuous venovenous hemofiltration (CVVH). Based on serial serum urea nitrogen concentration measurements, each patient's treatment course consisted of both steady state and non-steady state periods. Thirteen data sets were obtained from 11 critically ill patients treated with CVVH. The duration of therapy was 9.5 +/- 7.5 days (mean +/- SD). Serum urea nitrogen concentration fell from 114 +/- 32 mg/dl to a steady state value of 79 +/- 17 mg/dl (p < 0.0005). The urea distribution volume was 0.55 +/- 0.11 L/kg (range 0.29-0.73), and the urea generation rate 11.7 +/- 3.1 mg urea N/min (range 7.1-17.3). The steady state serum urea nitrogen concentration had a linear relationship to the rate of urea generation (r = 0.92). Urea kinetic analysis permitted the simultaneous determination of the urea generation rate and distribution volume, on an individualized basis, in patients with acute renal failure treated with CVVH.