Processing of the N-terminal initiator methionine or formylated methionine is an essential cellular process conserved from prokaryotes to eukaryotes. The proteolytic removal of N-terminal methionine from nascent peptides is catalyzed by a family of enzymes known as methionine aminopeptidases (MetAPs) and is essential for cell growth. METAP1 and METAP2 have different substrate specificity due to the differences in both size and shape of the active sites. As a member of the M24 family of metalloproteases, METAP1 plays an important role in G(2)/M phase regulation of the cell cycle and may serve as a promising target for the discovery and development of new anticancer agents.