Spores of Phanerochaete chrysosporium were inoculated in liquid culture medium in the presence of carriers with filtering properties (polyurethane foam, stainless-steel sieve). The immobilization mechanisms were investigated as well as the production of lignin-peroxidase and manganese-dependent lignin-peroxidase. The main immobilization mechanisms were Sound to be the formation of spore aggregates in suspension and the mechanical retention of these aggregates by the carriers. Adhesion of spores plays only a minor role in the immobilization process. Spore aggregation is very slow under laminar flow conditions. After retention, the fungus develops in the form of immobilized pellets dispersed in and on the carrier. The production of peroxidase varies by a factor up to 10 as a consequence of changing solely the arrangement of the carrier elements in shake flasks. For manganese-peroxidase, the production increases with an increase in the area of interface between the immobilized pellets and the culture medium. The results point to the importance of the cell microenvironment as a link between bioreactor design and cell activity.