For the removal of remaining amounts of endotoxin, sorbents with high selectivity for endotoxin are required. Typically, particulate sorbents with positively charged ligands, such as histidine, polymyxin B, poly-L-lysine and poly(ethyleneimine) (PEI), display moderate to high removal efficiencies in an environment of low ionic strength. It was found that polycationic ligands are most suitable to meet an endotoxin concentration which is below the threshold level required for parenteralia. Furthermore, protein recoveries close to 100% are obtained if the decontamination is performed at a pH close to the pI of acidic proteins. The high selectivity is probably caused by complexation of the polycationic ligand with the polyanionic endotoxin, leading to interactions with K D `10 ร9 M using PEI and assuming M r = 10 kDa for monomeric endotoxin; with BSA the same ligand reveals only K D = 4 ร 10 ร6 M. Using polymer-coated microfiltration membranes, immobilization of positively charged ligands leads to membrane adsorbers which are generally superior to chromatographic adsorbers and allow faster processing. Since immobilization takes place at polymer chains, low-molecular-weight ligands mainly add positive charges to the hydrophilic polymer. Consequently, membrane adsorbers with low-molecular-weight ligands, even DEAE, demonstrate similar selectivity to PEI or poly-L-lysine.