Using systems formed by particles of polyurethane foam of different densities soaked in an amylaceous effluent, the production of amylases by Aspergillus oryzae in solid state culture was studied by a complete factorial plan with four variables - support density, particle diameter, volume of liquid phase and substrate concentration. The empirical model obtained is consistent and allows a simple control of the response, superior in several respects to that of the corresponding submerged cultures. Moreover, it enables a mechanistic approach to the behaviour of the system, whose principal kinetic characteristics can be interpreted in terms of intra- and interparticular diffusional effects, which have a determining influence on basic state variables, such as water activity and gas transfer.