Objective: Comparison of three neonatal hemo(dia)filters (FH22, Gambro; Minifilter Plus, Amicon; Miniflow 10, Hospal) for removal of urea by venovenous hemofiltration (HF) and venovenous hemodiafiltration (HDF). Design: Filters were successively used for HF with two different blood flows (Qb = 8.3 and 16.6 ml/min) and for HDF with the two different blood flows and four dialysate flows (Qd = 0.5, 1.0, 2.0, and 3.0 l/h). Subjects: 21 anesthetized adult New Zealand White rabbits infused with urea. Main results: Urea clearance was significantly increased by HDF compared to HF regardless of blood flow, dialysate flow, and the hemo (dia)filter type except in the FH22 group, when blood flow was high and dialysate flow was 0.5 or 1.0 l/h. The FH22 filter allowed the best urea clearance during HF at high blood flow. During the HDF procedures, the Miniflow 10 allowed the highest urea clearance regardless of blood flow and dialysate flow.