Rice flour with varied water content (11, 15, 20 and 25%) was extruded in a Brabender single-screw extruder at different barrel temperatures (190, 205 and 220 degrees C). Growth and enzyme production during solid-state cultivation (koji making) of Aspergillus oryzae on the rice extrudate substrates and steamed rice were compared. The results revealed that the extent of mycelial propagation, the activities of amylase, neutral protease and acid protease, as well as the maltose-forming activity, varied according to the substrate used for koji making. Among the substrates tested, the greatest production of enzymes and growth of A. oryzae were found in koji prepared with a rice substrate extruded at 205 degrees C and with an 11% water content.