Improving hydrolases by site-directed mutagenesis continues to be important, but an alternative method-directed evolution - also gains favor. Directed evolution combines random mutagenesis with screening or selection for the desired property. Directed evolution is especially useful for cases like solvent tolerance or thermostability where current theories are inadequate to predict which structural changes will give improvement. Researchers have also recently made significant progress on several practical problems: how to maintain the high activity of proteases and lipases in nonpolar organic solvents, how to resolve amines, and how to efficiently recycle the unwanted enantiomer in kinetic resolutions. Besides the lipases and proteases, researchers are also developing new hydrolases, notably dehalogenases and epoxide hydrolases.