The adsorptive filtration technique using chitosan membranes was used to remove endotoxin (ET) from buffers and bothrops antivenom serum (F(ab')(2) fragments of equine antibodies). Macroporous chitosan membrane was prepared from chitosan using silica particles as porogen agent. The effects of solution conditions on the efficiency of endotoxin removal and protein recovery were studied. The ET concentrations were reduced to 0.58 and 71.6 EU/ml, respectively, when Tris-HCl pH 7.0 buffer with 18.6 and 8092.5 EU/ml was passed through the chitosan membrane. This buffer was used to evaluate ET removal in the presence of the equine F(ab')(2) fragments. The results showed that the presence of protein in the feed solution did not influence much the clearance of this membrane. Removal of 97% of the ET and recovery of 94 + of the F(ab')2 were obtained at an initial ET and F(ab')(2) concentration of 974.4 EU/ml and 18.6 mg/ml, respectively. (C) 2004 Elsevier B.V. All rights reserved.