We report a study made on a 5 kDa molecular weight cut-off (MWCO) polysulfone membrane (SPS 4005) for use in microdialysis sampling of starch enzymatic hydrolysates on-line coupled to column liquid chromatography with integrated pulsed electrochemical detection. Membrane characteristics were evaluated by examining both the membrane and membrane support layer using a scanning electron microscope (SEM). This study was made so as to elucidate the mechanism or mode by which a membrane exposed to different bioprocess conditions is either fouled or destroyed. The correlation of extraction fraction data with SEM was a confirmatory test for the observed change in the membrane characteristics. Examinations were made after keeping the membrane in pure water for 5, 10 and 30 min at room temperature or after perfusing the membrane with pure water continuously at room temperature, 60 and 90 degrees C for 24 h. Extraction fractions were evaluated at these temperatures to see applicability of the SPS 4005 membrane to high temperature bioprocesses. Scanning electron microscopy studies were also made on membranes used for sampling and sample clean-up during on-line monitoring of the hydrolysis of soluble starch (according to Zulkowsky) for 32 h, and the hydrolysis of wheat starch at room temperature, 60 and 90 degrees C for 6 h. Non-specific/directed protein-membrane interactions were evaluated by sampling maltoheptaose with a microdialysis probe fitted with a 10 mm SPS 4005 membrane, before and after treatment with an enzyme solution of Termamyl (endo-1,4-alpha-D-glucan glucanohydrolase EC 3.2.1.78).