Covalent coupling of chitosan to the activated membrane was performed after the reaction of the microporous nylon membrane with formaldehyde. Covalent linkage of chitosan was essential to improve the hydrophilicity and consequently reduced the non-specific interactions of the membranes. Cibacron Blue F3G A (CB F3GA) was then covalently immobilized onto the composite membrane to prepare affinity membrane for bilirubin removal. Different amounts of CB F3GA were attached on the composite membranes by changing the dye-attachment conditions, i.e. initial dye concentration, addition of sodium carbonate, and sodium chloride. The maximum CB F3GA content was obtained at 142.9 mumol/g membrane. Dye release in buffers showed a tight covalent bound of CB F3GA on the composite membrane. Bilirubin molecules interacted with the absorbents directly. Non-specific adsorption on the unmodified nylon membrane remains low, and higher bilirubin adsorption capacity, of up to 63.4 mg/g was obtained after CB F3GA immobilization. The effects of the CB F3GA content, temperature, ionic strength, and pH, as well as the adsorption isotherm were investigated in this study. The adsorption capacity increased with increasing the temperature while decreased with increasing the NaCl concentration and a peak at about pH 6.0 was observed during the corresponding experiment. The adsorption isotherm fitted the Freundlich model well. Experiments on regeneration and dynamic adsorption were also performed. (C) 2003 Elsevier B.V. All rights reserved.