Aims: Evaluate the use of polyethyleneimines (PEIs) as membrane permeabilizers to improve the responses and sensitivity of a bacterial bioreporter strain to viologens. Methods and Results: The responses from E.coli str. EBS, i.e., E.coli BW25113 carrying plasmid pSDS, when exposed to five different viologens were characterized, as were the toxicities of seven different PEIS, including two linear and five branched species. Based on these results, benzyl viologen led to the greatest responses, and 0.8-kDa branched PEI (BPEI) was the least toxic of the PEIs tested and, therefore, both were selected for the subsequent tests. The bioluminescence and relative responses from E.coli str. EBS exposed to various concentrations of 0.8 kDa BPEI identified 400 mg l(-1) as the optimal concentration. Using this concentration, tests were performed with all five of the viologens. Conclusions: The responses from E.coli str. EBS to the viologens were improved, with the maximum relative bioluminescence values increasing between 5.6 and 16.5-fold. The minimum detectable levels for four of the viologens were likewise improved 2- to 4-fold. Significance and Impact of Study: Improving bacterial membrane permeability in a controlled manner using BPEIs can improve biosensing of toxic compounds, as well as be used in biofuel and bioenergy applications where membrane permeability to a solute is important.