The kinetics of bio-oxidation by a microbial ensemble of a model mixture of contaminants that mimicked the ground-water pollution plume at an existing contaminated site was investigated. Phenol at 50 mg/l and a mixture of ten organic contaminants (MOC) (benzene, tetrachloromethane, trichloroethylene, toluene, o-xylene, 1,4-dichlorobenzene o-cresol, nitrobenzene, naphthalene and 2,6-dichlorophenol) at individual concentrations ranging from 150 mu g/l to 600 mu g/l were the components of the model mixture. The microbial ensemble consisted of at least three Pseudomonas spp, isolated from the polluted site. Patterns of oxygen uptake rate (OUR) for the oxidation of phenol alone and with added MOC were treated mathematically. The values for kinetic parameters that gave the best fit to the data were respectively 11.29 and 15.03 ml O-2 h(-1) (mg protein)(-1) for the OUR maximum (OUR(max)), 75.89 mg/l and 33.66 mg/l for the saturation constant (K-s), 105.92 mg/l and 36.44 mg/l for the inhibitor constant (K-i), and 89.66 mg/l and 35.02 mg/l the substrate minimum inhibitory concentration (S-mic). This study also scrutinised interference between the two components of the model mixture of contaminants (phenol and MOC) on the basis of variations in kinetic patterns. MOC was shown to be toxic at milligram per litre levels. The microbial ensemble increased phenol oxidation in response to MOC, possibly to obtain the energy to overcome this toxic effect. This was indicated by an acceleration of phenol oxidation in response to increasing concentrations of MOC and higher OUR(max) for oxidation of phenol in the presence of MOC. The toxicity of MOC also resulted in enhanced vulnerability of the microbial ensemble to a phenol inhibitory effect, indicated by the diminution of K-i and S-mic. The microbial ensemble showed high resistance to inhibition by the sole presence of phenol possibly because of adaptation to toxic features of MOC during the processes of enrichment and cultivation.