An alkaline protease from a facultatively thermophilic and alkalophilic strain of Bacillus brevis has been studied. The enzyme from a shake flask culture displayed maximum activity at pH 10.5 and 37 degrees C. The extracellular production of the enzyme, its thermostable nature and compatibility with most commercial detergents are features which suggest its application in detergent industry. The organism utilized several carbon sources for the production of proteases, lactose was the best substrate followed by glucose and sucrose. Among the various organic nitrogen sources, soyabean meal was found to be the best. The protease was stable at 25 degrees C for 288 h whereas, at 50 and 60 degrees C, the half lives were 60 and 7 h, respectively. The thermostability of the protease was enhanced by modifying its microenvironment. Acetate salts of Ca2+ and Na+ increased thermostability and protected against autolysis. Addition of Ca2+ (10 mM) and glycine (1 M) individually and in combination was found to be effective in increasing the half life of protease by many folds. The enzyme retained more than 50% activity after 4 days at 60 degrees C in the presence of both Ca2+ (10 mM) and glycine (1 M). The enzyme showed compatibility at 60 degrees C with commercial detergents such as Aerial Microshine(R), Surf excel(R), Surf Ultra(R) and Rin(R) in the presence of Ca2+ and glycine. This enzyme improved the cleaning power of various detergents. It could remove blood stains completely when used with detergents in the presence of Ca2+ and glycine.