The Z-curve is a three-dimensional curve that constitutes a unique 
representation of a DNA sequence, i.e., both the Z-curve and the given DNA 
sequence can be uniquely reconstructed from the other. We employed Z-curve 
analysis to identify one replication origin in the Methanocaldococcus jannaschii 
genome, two replication origins in the Halobacterium species NRC-1 genome and 
one replication origin in the Methanosarcina mazei genome. One of the predicted 
replication origins of Halobacterium species NRC-1 is the same as a replication 
origin later identified by in vivo experiments. The Z-curve analysis of the 
Sulfolobus solfataricus P2 genome suggested the existence of three replication 
origins, which is also consistent with later experimental results. This review 
aims to summarize applications of the Z-curve in identifying replication origins 
of archaeal genomes, and to provide clues about the locations of as yet 
unidentified replication origins of the Aeropyrum pernix K1, Methanococcus 
maripaludis S2, Picrophilus torridus DSM 9790 and Pyrobaculum aerophilum str. 
IM2 genomes.