Two whole-cell biosensors were constructed to detect the in situ biodegradation of polychlorinated biphenyl by chromosomal insertion of a mini-Tn5-Km r -Pm::gfpmut3-T 0 -T 1 construct into P. fluorescens. In vitro tests showed that the expression of the Pm promoter depended on the growth phase of the biosensors and the concentration of chemical inducers; chlorinated benzoic acid derivatives. A linear relationship between the fluorescent intensity and the log 10 concentration of the inducer was observed. One biosensor (F113L::1180gfp) had the ability to degrade PCBs to relevant chlorobenzoic acid derivatives and to induce expression of Gfp. The second biosensor (F113gfp), which cannot degrade PCBs, shows fluorescence after induction by chloro-benzoic acid derivatives. By using these two biosensors, PCB degradation could be detected in vitro and in soil.