The interconversion of 3-phosphoglycerate and 2-phosphoglycerate during glycolysis and gluconeogenesis is catalyzed by phosphoglycerate mutase (PGM). In bacteria and eukaryotes two structurally distinct enzymes have been found, a cofactor-dependent and a cofactor-independent (iPGM) type. Sequence analysis of archaeal genomes did not find PGMs of either kind, but identified a new family of proteins, distantly related to iPGMs. In this study, these predicted archaeal PGMs from Pyrococcus furiosus and Methanococcus jannaschii have been functionally produced in Escherichia coli, and characterization of the purified proteins has confirmed that they are iPGMs. Analysis of the available microbial genomes indicates that this new type of iPGM is widely distributed among archaea and also encoded in several bacteria. In addition, as has been demonstrated in certain bacteria, some archaea appear to possess an alternative, cofactor-dependent PGM.