The beta‐glucosidase inThermomonspora curvatawas stabilized against thermal denaturation by a soluble intracellular factor. This factor had an apparent molecular weight of 6kD, was resistant to proteolytic digestion, stable to boiling but was inactivated by autoclaving. It had little effect on beta‐glucosidase maximal velocities or substrate affinity but it reduced the enzyme inactivation rate five‐fold at