We determined the elimination characteristics of procalcitonin (PCT) during continuous veno-venous hemofiltration (CVVHF) and the resulting effect on PCT plasma levels. A prospective study was conducted in patients with sepsis and acute oliguric renal failure, treated with CVVHF using a polysulfone membrane (Baxter Renaflo II PSHF 1200). Patients had sepsis and PCT plasma levels > 4 ng ml(-1) (n = 26). PCT was measured in the pre- and post-filter plasma and the ultrafiltrate at 0, 5, 10, and 15 min and 1, 2, 4, 6, 12, and 24 h after setup of CVVHF. PCT sieving coefficient was 0.24. Elimination of PCT, however, depended on the duration of filtration, because filter adsorption was the main mechanism of PCT clearance during the first hour of hemofiltration, finally increasing to a clearance of PCT into the ultrafiltrate of 2.8-5.5 mL/min after 2 h. PCT plasma levels were not significantly altered during CVVHF (96% of the initial concentration after 24 h, P = 0.72). Similar to what has been observed with cytokines and other proteins of a comparable molecular weight, PCT is removed from the plasma during CVVHF, but plasma PCT levels are unchanged. Thus, PCT can be used as a diagnostic parameter even in patients with acute renal failure undergoing CVVHF.