Batch cultures of Pseudomonas fluorescens (strain P2a) maintained under carbon-limiting conditions in the presence of chrysene and other aromatics, survived starvation with no detectable changes in cell number for at least 4 months. P2a also demonstrated high dioxygenase levels after growth on benzoate and catechol. To characterize this strain further, early stationary-phase cells were resuspended in fresh mineral medium containing different aromatics, to evaluate enzyme expression in the presence of high-molecular-mass (isocyclic and heterocyclic) compounds. Results demonstrated effects on catechol 1,2-dioxygenase modulation by the model compounds used, confirming a low substrate specificity for this enzyme. The increases of specific activity observed in the presence of heterocyclic compounds were higher than those observed with isocyclic compounds.