A number of culture conditions for protease production by Aspergillus oryzae NRRL 2160 on solid substrates were investigated. The pH of the medium and the substrate markedly affected protease production. High protease yield was obtained when the fungus was cultivated for 72-96 h on rice hulls: rice bran (7:3), at an initial pH of 7.0. Maximal protease production was achieved at an initial moisture content of 35-40%, corresponding to a water activity range of 0.982-0.986. Casein and gluten were effective inducers. Polyethylene bags proved to be promising containment systems for solid state cultivation.