Bacterial phenol-oxygenating activity was measured at phenol concentrations from 0.3 mu M to 20 mM. The kinetic parameters in Haldane’s formula, apparent K-s, K-SI, and V-max for the activity were determined. All the strains isolated from a continuous culture enriched by a low concentration of phenol expressed phenol-oxygenating activities with low apparent K-s (below 1 mu M).