Studies on the extraction of protease in the solid state fermentation of wheat bran by Rhizopus oryzae, were conducted. Using distilled water (DW) as extractant, the optimum volume was 5 ml/g bran. An extraction or soaking time of 2 h at 4 degrees C was sufficient to extract out nearly 90% (52.5 U/g bran) of enzyme while complete extraction was attained in 10 h (58.7 U/g bran). With the optimum extractant Volume of 5 ml DW/g bran, most of the enzyme was recovered in one extraction (60 U/g bran) while repeated extractions yielded very little enzyme (5 and 2.8 U/g bran in the second and the third extractions, respectively). An attempt has been made to explain these results with the leaching or dissolving equation. Among other studies, while extractant pH did not affect recovery, extraction with neutral potassium phosphate buffer resulted in increased yields compared to DW and was also affected by the molarity of the buffer, with the maximum increase (1.42 times) being effected by 0.6 M buffer. Another major study was the investigation of protease production in relation to growth as seen in ＇soft gel culture＇. Growth in soft gel culture was almost linear although colony growth on malt extract agar was radial. Production did not appear to be associated with growth. (C) 2000 Elsevier Science Ltd. All rights reserved.