This study examined heat shock proteins (hsps) of the periodontal pathogen Prevotella intermedia and the closely related species, Prevotella nigrescens and Prevotella corporis. After heat shock at 45 degrees C for 5 min, cell-free extracts were analysed by SDS-PAGE and Western blotting with polyclonal antibodies against Escherichia coli hsps. P. intermedia, P. nigrescens and P. corporis all expressed a DnaK homologue. The P. nigrescens DnaK was of a similar molecular mass to E. coli DnaK (70 kDa), whilst those of P. intermedia and P. corporis were approximately 69 kDa. DnaJ homologues were expressed in each species; however, no homologue of GrpE was detected. P. intermedia DnaK was purified to homogeneity by ion-exchange and affinity-chromatography, and was shown to restore activity of denatured luciferase. This molecular chaperone activity was enhanced by E. coli DnaJ and GrpE which are components of the Hsp70 molecular chaperone machine.