Posttranslational protein modifications affect the function or the activity of proteins and exhibit important mechanisms in regulating cellular events. A broad spectrum of modifications is known, including redox-dependent alterations. During the last decade, covalent binding of nitric oxide (NO) to protein cysteines, termed S-nitrosylation, seems especially an evident process for redox-related signaling. To reveal potential target proteins for S-nitrosylation, the biotin switch method gains more and more in importance. This technique is a tool used for analyzing the nitrosylome as well as the examination of single candidates. It is based on substitution of the NO group by a biotin linker that simplifies the detection and the purification of recently S-nitrosylated proteins in a three-step procedure.