A Streptomyces sp. was isolated that produced novel thermoalkalotolerant cellulase activity after growth on crystalline cellulose at 50 degrees C. Three major components of the cellulases (CMCase, Avicelase and cellobiase) were produced with maximal activities (11.8, 7.8 and 3.9 IU/ml) and maximum specific activities 357, 276 and 118 IU/mg protein, respectively, after 120 h growth. Maximum CMCase activity was between 50 and 60 degrees C measured over 3 h. The enzyme also retained 88% of its maximum activity at 70 degrees C and pH 5, and 80% of the activity at pH 10 and 50 degrees C when assayed after 1 h. After incubation at 40 degrees C for 1 h with commercial detergent (Tide) at pH 11, 95% activity was retained. The enzyme mixture produced glucose from crystalline cellulose.