A simple form of immobilisation (support) of two pellet-form mycelial microorganisms on powdered core of maize cob is described. At a constant weight of support, the pellet number and size and, therefore, the pellet's surface to volume ratio were highly conditioned by the mean diameter of the support particles. Independently of the chemical nature of the support, an increase in surface to volume ratio produced an enhancement of the microbial metabolic activity, up to a point at which the small pellet size approximated the organisms in the culture to the filamentous form and reversed the tendency. Optimisation of the metabolic activity, with an important increase in the production of extracellular amylases, could be obtained by varying support diameter and amount per unit volume of culture.