As measured by the toluene-induced bioluminescent response of Pseudomonas putida TVA8 in batch experiments, toluene dioxygenase (Tod) enzyme activities are dependent on toluene concentration between 0 and 30 mg/L. To provide a measure of the Tod activity for use in Michaelis-Menten competitive-inhibition kinetics, a correlation between toluene concentration and induced Tod activity as measured by an induced bioluminescent response of P. putida TVA8 is presented as a nondimensional Tod activity parameter. A packed-bed, radial-flow bioreactor (RFB) using the bioreporter P. putida TVA8A serves as the model system for studying the effect of the enzyme activity parameter on model predictions of vapor-phase toluene oxidation and trichloroethylene (TCE) cometabolism. Mass balances were performed on a differential section of the RFB to describe the radial transport of vapor-phase toluene and TCE through a bulk gas phase and the concomitant biological reaction in a stationary biofilm phase. The finite-element Galerkin weak-statement formulation with first-order basis functions was used to find the optimum solution to the highly nonlinear, coupled equations. For this RFB system with toluene concentrations less than 1 mg/L in the bulk gas phase, the Tod activity parameter enables accurate predictions of steady-state TCE degradation rate (0.27 mug TCE/min).