In addition to pure synthesis, the »Cell-free protein synthesis« research group offers a reliable method for introducing chemically modified amino acids into the cell-free synthesized proteins. The amber suppression method is used to introduce amino acids with a wide variety of reactive groups at site-specific positions. Furthermore, we use click chemistry to couple fluorescent dyes, sugar structures, PEGylations and biotinylations to the reactive groups of the introduced amino acids. Our method is well suited for the structural analysis and functional determination of membrane proteins, but also for the screening of novel ligands and therapeutics. In addition, proteins can be selectively modified to introduce new functions for therapeutic purposes.