A comparative study was carried out on the production of neutral protease using agro-industrial residues as substrate in solid-state fermentation (SSF) and submerged fermentation (SmF). Seven fungal cultures, viz. three strains of Aspergillus oryzae and four strains belonging to Penicillium sp, P. funiculosum, P. funiculosum, P. pinophilum, P. aculeatum were evaluated using a plate assay for enzyme production, which showed a strain of A. oryzae NRRL 1808 as the most useful culture. Several agro-industrial residues (wheat bran, rice husk, rice bran, spent brewing grain, coconut oil cake, palm kernel cake, sesame oil cake, jackfruit seed powder and olive oil cake) were screened for neutral protease production in SmF and SSF. In both systems, wheat bran was the best substrate. Best results in SSF were obtained in a medium having an initial moisture content of 43.6%, when inoculated with 1 ml of spore suspension (8 x 10(8) spores) and incubated at 30 degrees C for 72 h (31.2 U enzyme per gram of fermented substrate - U/gds). SmF medium (pH 7.5) containing 2% (w/v) wheat bran, when inoculated with 3 ml of spore suspension and incubated at 30 degrees C and 180 rpm for 72 h gave maximum enzyme yield of 8.7 U/gds. A comparative evaluation of protease yield by the two fermentation systems showed 3.5-fold more enzyme production in SSF, clearly demonstrating the superiority of SSF over SmF. (c) 2005 Elsevier Ltd. All rights reserved.