The stabilization of invertase by its incorporation in aqueous trehalose and polymer solutions, followed by freeze-drying and desiccation to ＇zero＇ moisture content was studied. The dried amorphous preparations of trehalose, maltodextrin (MD; DE = 10.9), and poly(vinyl)pyrrolidone (PVP), molecular weights 360000, 40000 and 10000, greatly protected invertase-as compared with its behavior in liquid solution-from heat inactivation at elevated temperatures. Significant invertase inactivation was observed in heated PVP and MD matrices kept well below their glass-transition temperature. Under glassy conditions the extent of enzyme protection by MD and PVP systems was related to their glass-transition temperature (T-g) since systems of higher T-g afforded better protection. However the data for trehalose deviated from this behavior since invertase stabilization was higher than expected on the basis of the results obtained with polymer matrices. Present results suggest that invertase inactivation in dried amorphous systems cannot be adequately explained by the glass-transition theory and this is particularly true for trehalose, for which some additional mechanism of enzyme protection is likely to operate.