We do not currently use peptide mass fingerprinting alone for protein identification, but often use an identification approach which compares lists of best-matching proteins generated by AA composition identification and peptide mass fingerprinting techniques (see MultiIdent tool for details). For this approach, one sample is subjected to the amino acid analysis procedure to generate a list of best matching proteins, and a duplicate sample is subjected to peptide mass fingerprinting to generate an independent list of best matching proteins. Identification is achieved when lists of best-matching proteins are then compared for identical database. This technique has two main applications. Firstly, in situations where proteins are blocked at the N-terminus and cannot be used for "sequence tagging", and secondly where proteins are being identified over large or small phylogenetic distances across species boundaries. As peptide mass fingerprinting has a sample throughput similar to AA analysis, this combined identification approach is suitable for rapid protein identification.