Carboxypeptidase from the archaebacterium Sulfolobus solfataricus is heat stable with an optimal enzyme activity at 85 degrees C (Colombo et al., 1992). However in the absence of glycerol and beta-mercaptoethanol, at 50 degrees C, the enzyme undergoes a slow thermal inactivation upon dilution in an aqueous buffer at pH 6.5. This loss of activity can be inhibited when the enzyme is maintained at high pressure. At higher temperatures, higher pressures (up to 400 MPa) are required to maintain the enzyme in its active state.