The highest productivity (20 IU l(-1) h(-1)) of beta-glucosidase by a mutant of Cellulomonas biazotea was 2.5-fold more than that of the parent organism. The enzyme had a lower activation energy (57 kJ mol(-1)) than the native enzyme (68 kJ mol(-1)). The enzyme from the mutant had enthalpy and entropy values for irreversible intactivation of 95.6 kJ mol(-1) and 60 J.mol(-1) K-1 compared with 108 kJ mol(-1) and 86 J mol(-1) K-1 for the native enzyme suggesting that the mutation had stabilized the enzyme.