In this paper evidence is given that in a strain of Pseudomonas fluorescens able to grow on styrene as the sole carbon source, the degradation pathway of styrene is inducible and plasmid dependent. The plasmid, which we have called pEG is self-transmissible between Pseudomonas strains and has a size of 37 kb. A restriction map has been constructed and evidence for an inducible transcription of two separate regions of the plasmid has been obtained.