Kallikrein is involved in the generation of bradykinin during extracorporal circulation, that is believed to play an important role in cases of anaphylactic shock during hemodialysis. Therefore, a method for the assessment of kallikrein generation was developed, based on the chromogenic substrate S-2302. Comparison of kallikrein-like activity on glass using citrate or heparinized plasma demonstrated enhanced activity in the presence of heparin. The applicability of the assay, and the time course of kallikrein generation was demonstrated with glass and cuprophan. Membranes based on pure polyacrylonitrile, or its copolymers differing in their content of acrylic acid, 2-hydroxyethyl acrylate, and allylsulphonate were investigated with respect to kallikrein-like activity, and physicochemical surface properties. It was found that high content in 2-hydroxyethyl acrylate, and acrylic acid caused a substantial activation of the contact system while low content in allylsulphonate (less than 2 mol%) did not result in enhanced kallikrein-like activity. The activating materials were characterized to be highly wettable, and had the most negative zeta potentials.