An enhanced resistance to thermal denaturation was investigated for enzymes immobilized within hydrophobic semi-solid matrices compared with both free enzymes and polymer-entrapped enzymes. The bioelectrodes based on the immobilization of glucose oxidase, lactate oxidase, alcohol oxidase, polyphenol oxidase, peroxidase and L-amino acid oxidase within a carbon-paste matrix were constructed to examine their thermal stabilitiy at 60 degrees C or 80 degrees C. The rhodium/glucose oxidase-containing carbon-paste electrode was found to offer a remarkable stability when incubated at 60 degrees C over a long period of 4 months, with only a decrease of approx. 15% in activity. The comparative studies suggest that thermal stabilization established by this enzyme-immobilization procedure varies with the enzyme's inherent stability, the incubation temperature and the immobilizing reagent, such as pasting liquid.