During the MVT'90 US oceanographic cruise, various samples (pieces of hydrothermal chimneys, Pompei worms tubes) were collected from deep-sea hydrothermal vents of the East Pacific Rise. They led to the isolation of 125 thermophilic, heterotrophic, sulfur-reducing and anaerobic strains. The results indicated an acidophilic behaviour of the most thermophilic strains (97 degrees C). Taxonamic study of the 38 most thermophilic isolates revealed 2 sub-groups depending on isolation temperatures and G + C% contents of genoms. DNR/DNA hybridization data with previously described Archaea of the genera Thermococcus, Pyrococcus and Staphylothermus showed an important biodiversity.