The knowledge of critical process-relevant genes can be used for an improved control of bioprocesses. So far bioprocess-relevant marker genes can be analyzed by established expression analysis methods only off-line. In this study, an alternative approach for a potential at-line monitoring of gene expression during bioprocesses is suggested. This approach is based on the measurement of specific mRNAs on an electric DNA-chip in connection with a magnetic bead-based sandwich hybridization. In order to allow an at-line measurement of specific mRNAs an improved method for a fast and partially automated isolation of high quality-RNA samples was developed. The expression analysis of the electric DNA-chip was compared with optical DNA micro arrays and the real time RT-PCR for three selected processrelevant genes of Bacillus subtilis. We demonstrate that the mRNA analysis by means of the electric DNA-chip gives similar results compared to the micro array analysis and the real time RT-PCR technique. (c) 2005 Wiley Periodicals, Inc.