The synthesis of an azobenzene amino acid (aa) for use as a photo-inducible conformational switch in polypeptides is described. The compound can be easily incorporated into an aa sequence by solid-phase peptide synthesis using standard 9-fluorenylmethoxycarbonyl methods. A reversible conformational change of the peptide backbone is induced by switching between the cis and trans configurations of the azobenzene moiety by irradiation with light of suitable wavelength. Thermal cis --> trans isomerization of this azobenzene aa is slow, enabling detailed structural investigations of the modified peptides, e.g., using NMR techniques. The total time for the synthesis of the photoswitch is typically 4 d, with an overall yield of 40-50%.