['Continuous veno-venous haemofiltration (HF) with high permeability (HP) haemofilters is a novel approach in the adjuvant therapy of septic patients. HP haemofilters are characterized by an increased pore size which facilitates the filtration of inflammatory mediators. The present study examines whether HP-HF has an impact on peripheral blood mononuclear cell (PBMC) proliferation and whether ultrafiltrate can alter PBMC function in isolates from healthy volunteers.', 'Twenty-eight septic patients with acute renal failure were randomly allocated to either HP-HF or conventional HF (C-HF). HP-HF was performed with a newly developed high-flux polyamide membrane (P2SH) with a nominal cut-off point of 60 kDa. For C-HF, a high-flux polyamide haemofilter (Polyflux 11S; cut-off, 30 kDa) was used.', 'Septic patients demonstrated a significantly reduced proliferation of anti-CD3-stimulated PBMCs compared to healthy controls (P = 0.016). Initiating HF led to a restoration of the PBMC proliferation in HP-HF but not in C-HF. Exposing PBMCs isolated from healthy donors to ultrafiltrates from patients with sepsis demonstrated a significant suppressive effect of HP ultrafiltrates on the anti-CD3-stimulated PBMC proliferation (P = 0.011). Ultrafiltrate from patients with sepsis who received C-HF had no impact on PBMC proliferation.'] Does high permeability haemofiltration improve peripheral blood mononuclear cell proliferation in septic patients with acute renal failure?