The dramatic activation of enzymes in nonaqueous media upon co-lyophilization with simple inorganic salts has been investigated as a function of the Jones-Dole B coefficient, a thermodynamic parameter for characterizing the salt's affinity for water and its chaotropic (water-structure breaking) or kosmotropic (waterstructure making) character. In general, the water content, active-site content, and transesterification activity of freeze-dried subtilisin Carlsberg preparations containing >96% w/w salt increased with increasing kosmotropicity of the activating salt. Degrees of activation relative to the salt-free enzyme ranged from 33fold for chaotropic sodium iodide to 2480-fold for kosmotropic sodium acetate. Exceptions to the general trend can be explained by the mechanical properties and freezing characteristics of the salts undergoing lyophilization. The profound activating effect can thus be attributed in part to the stabilizing (salting-out) effect of kosmotropic salts and the phenomenon of preferential hydration.