A simple staining procedure, associated with image analysis, was used to discriminate two zones (the filamentous zones and the compacted cores) in aggregates of fungal biomass according to their accessibility for an agent of the medium. The application of the method to batch fermentations of Schizophyllum commune showed a higher proportion of loosely entangled particles (clumps) and thinner filamentous outer zones obtained at a high agitation speed (500 rpm) compared to low agitation speeds (120-200 rpm).