The organic solvent-tolerant strain K protease was purified to homogeneity by ammonium sulphate precipitation and anion exchange chromatography with 124-fold increase in specific activity. The molecular mass of the purified enzyme as revealed by SDS-PAGE electrophoresis is 51,000 Da. The strain K protease was an alkaline metalloprotease with an optimum pH and temperature of 10 and 70 degrees C, respectively. The enzyme showed stability and activation in the presence of organic solvents with log P-a/w values equal or more than 4.0. After 14 days of incubation, the purified protease was activated 1.11, 1.82, 1.50, 1.75 and 1.80 times in 1-decanol, isooctane, decane, dodecane and hexadecane, respectively. (c) 2006 Elsevier Inc. All rights reserved.