The vent shrimps, Mirocaris fortunata and Rimicaris exoculata, live in a highly fluctuating thermal environment and undergo frequent temperature bursts. As a first step in the investigation of the response to heat stress, this work aimed to characterize stress proteins in these two species. Complementary deoxyribonucleic acid (cDNA) clones encoding a 70-kDa heat shock protein (HSP) were isolated and characterized from M. fortunata and R. exoculata. The cDNA clones were of 2055 and 1941 base pairs in length, and contained a 2018-bp complete open reading frame (ORF) and a 1785-bp partial coding sequence, respectively. The amino acid sequences corresponding to these ORF are 645 residues in length for M. fortunata and 595 for R. exoculata, and were clearly characterized as members of the HSP70 family. The C-terminal extremity would identify R. exoculata sequence as a cytoplasm HSP70. The relationships between the crustacean HSP70 sequences were examined by two phylogenetic methods, i.e. Maximum Likelihood and Bayesian methods. The resulting trees suggested that M. fortunata sequence may correspond to constitutively expressed HSP70, named HSC70, whereas R. exoculata sequence may correspond to an inducible form of HSP70. The HSP70 sequences from the hydrothermal shrimps proved to be very similar to the other homologous shrimp sequences, except for the presence of an insertion of unknown function in the ATPase domain of R. exoculata sequence.