The monoaldehyde derivative of beta-cyclodextrin was attached to trypsin via reductive alkylation with NaBH4. The thermostability was enhanced from 49.5 degreesC to 60 degreesC for modified trypsin. The activation free energy of thermal inactivation at 50 degreesC was increased by 3.2 kJ mol(-1). The conjugated enzyme retained 100% of its initial activity after 3 h incubation at pH 9.