A decade after the discovery of histones in Archaea, there is now also a biochemical description of the archaeal nucleosome. A tetrameric core of archaeal histones is encircled by approximately 80 bp of DNA, and nuclease digestions indicate that adjacent archaeal nucleosomes exist in vivo compacting archaeal genomic DNA. Most Eukarya employ a similar structure to organize their chromosomal DNA, the eukaryal nucleosome, with a histone octamer and 146 bp of DNA. Here we compare the properties of both nucleosomes in terms of DNA packaging and the accessibility of the packaged DNA for transcription.