Aspergillus oryzae CFTRI 1480, an isolate from a spoiled moist sample of casein, produced 59,105 units of an extracellular proteinase/g dry mouldy bran (DMB) at 72 h in an arbitrarily formulated wheat bran medium in a solid state fermentation system. The enzyme production was significantly affected by mineral salt content and pH of the liquid used for moistening the wheat bran. Enzyme titres were enhanced 1.34-fold with the addition of 0.4% corn starch. Optimization of key parameters, i.e., initial moisture content, age and size of inoculum, increased the enzyme production to 191,869 units/g DMB and reduced the fermentation time to 48 h. Such high titres in a simple medium, surpassing most of the literature reports, indicate the industrial importance of the culture. The properties of acetone-precipitated enzyme, viz, the optimum pH of 10.0, more than 95% activity between pH 7.0 and 10.0, temperature optimum at 55 degrees C and more than 90% activity between 10 and 27 degrees C, are similar to those of commercially available fungal proteinases employed in animal feed, leather and other industries.