Purified endo-beta-1,4-xylanase of Bacillus amyloliquefaciens MIR 32 retained 100% of its activity after 4 days of incubation at 50 degrees C. Sorbitol (400 mg cm(-3)) produced a 63-fold increase in the half-life of the enzyme at 65 degrees C, which was only 29 min at this temperature in the absence of the polyol. This thermal stabilizing activity increased exponentially in respect to sorbitol concentration in the range 250-400 mg cm(-3) and was dependent on the pH, showing a maximum at pH values between 5.25 and 8.0. The circular dichroism (CD) thermal scanning profile (50 degrees C h(-1)) at 224 nm showed that changes in the secondary structure of xylanase started at 65 degrees C, while in the presence of sorbitol (400 mg cm(-3)) these modifications started at 80 degrees C. This study indicated that sorbitol might be a valuable stabilizer for the use of beta-xylanase from B. amyloliquefaciens at high temperatures.