Heat shock proteins (HSP) belong to a group of proteins which have increased expression when the cells are exposed to elevated temperatures. Heat shock proteins from the endophytic nitrogen-fixing bacterium Herbaspirillum seropedicae were examined using two-dimensional electrophoresis (2-DE). Colloidal Coomassie G250 was used to visualize proteins which were excised, subjected to in-gel trypsin digestion and analyzed using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Monoisotopic masses were used to search the genome sequence of Herbaspirillum seropedicae (www.genopar.org) using ProteinProspector. The searches were performed with a maximum mass tolerance of 200ppm, and identification was considered positive with a minimum of 7 peptide matches, and a mowse score 10³ times greater than the second candidate. The same spot from at least two different gels were excised and analyzed to confirm protein identification.  Ten protein spots representig 7 different proteins (DnaK, IbpA, GroES, UspA, GroEL, Phasin and nucleoside diphosphate kinase) were found to be highly expressed in H. seropedicae culture subjected to 42^o C for 15 minutes. The IpbA protein was identified in three different spots, suggesting post-translational modifications. The universal stress protein UspA also displayed two different isoforms of distinct pI, possibly due to phosphorylation. The abundance of the putative phosphorylated form increased upon the heat shock, suggesting a shift in activity under the stressing condition. The proteins phasin and an nucleoside diphosphate kinase were also induced on the heat shock treatment, and this is the first report on their involvement in heat shock response in bacteria.