Poly(ethylene) hollow-fibre membranes with immobilised Cibacron Blue F3G-A were obtained in four different ways from epoxy-activated fibres. Membranes with a maximum capacity of 26 mg lysozyme ml(-1) and a dye density of 52 mu mol ml(-)1 were obtained when ammonia was used to open the epoxy group before dye immobilisation. Pure water flux of the modified membranes at 1 bar pressure was 1.0 cm min(-1), thus meaning only a reduction of 1.5-fold with regard to the unmodified membranes. The support-dye bond was stable as judged by the unmodified capacity of the membranes and the negligible amount of dye leaked after 520 h of exposure to 6 M urea in 0.5 M NaOH.