Why is the enthusiasm for protein engineering so high today? Protein engineering plays important role in the modern protein crystallography. Using the protein engineering was possible preparation useful mutations for heavy-atom derivatization. Site direct mutagenesis alows to improve quality of the crystals too. The most interesting application of the protein engineering techniques for phasing macromolecular structures is ,in the last years, overexpression selenomethionyl proteins. In the last decade over 20 (based on the PDB data) protein structures have been solved using selenomethionine-labelled proteins and MAD. Protein engineering has at last its place as a standard tool of macromolecular crystallography.