Automated N-terminal sequence analysis involves a series of chemical reactions that derivatize and remove one amino acid at a time from the N-terminus of purified peptides or intact proteins. At least several picomoles of a purified protein or 10 to 20 pmol of a purified peptide with an unmodified N-terminus is required to obtain useful sequence information. In recent years, the demand for N-terminal sequencing has decreased substantially as some applications for protein identification and characterization can now be more effectively performed using mass spectrometry. However, N-terminal sequencing remains the method of choice for verifying the N-terminal boundary of recombinant proteins, determining the N-terminus of protease-resistant domains, identifying proteins isolated from species where most of the genome has not yet been sequenced, and mapping modified or crosslinked sites in proteins that prove to be refractory to analysis by mass spectrometry.