Stimulatory effects of three different intermediate metabolites (1-hydroxy-2-naphthoate, salicylate, and catechol) as potential inducers on phenanthrene degradation were investigated using two different bacteria (Pseudomonas putida ATCC 17484 and Burkholderia cepacia PB12). The relative induction capacity was high in the sequence of 1-hydroxy-2-naphthoate, salicylate, and catechol in both strains. The highest of up to 12 times increase of the induction was obtained by the addition of 1-hydroxy-2-naphthoate in the strain PB12, compared with the control where no exogenous inducer was added. The induction capacity of the potential inducers was closely related with the number of oxygenations required per electron equivalents in one mole of the inducer.