Here we report on the effect of the bacterial elicitor harpin from Pseudomonas syringae on Arabidopsis thaliana with an emphasis on transcriptional profiling and on changes of the mitochondrial proteome. Interestingly, of the currently about 400 identified mitochondrial proteins, transcriptional profiling by genome-wide DNA-microarray analyses revealed a total of 192 genes that showed significant changes in transcript abundance in response to the bacterial elicitor. The most dramatic changes were observed for the mitochondrial protein import apparatus of which 70% of all genes were induced. Proteomic analyses by 2D-PAGE and MALDI-TOF Mass Spectrometry for peptide fingerprint analysis confirmed the corresponding changes within the mitochondrial proteome in 28 cases. Strikingly, we found an accumulation of virtually all members of the TCA cycle. In sum, our results point to an involvement of mitochondria in the response of plant cells to the harpin elicitor, which becomes apparent both at the transcriptomic as well as proteomic level.