Many crystals of biological macromolecules have been successfully studied by atomic force microscopy (AFM) to analyze either their topographic structure or their mechanism of crystal growth. Unfortunately, a major problem for this kind of structural investigation, in particular for protein crystals, has been their immobilization to a substrate surface. In this paper, we report how to immobilize catalase monocrystals at the highly oriented pyrolytic graphite surface using polypyrrole films as a conductive cement. AFM coupled with an electrochemical system and optical microscopy techniques were used to monitor the in situ immobilization of a catalase single crystal for future physicochemical and structural investigations on soft biological single crystals. (C) 2002 The Electrochemical Society.