The effects of prolonged toluene exposure and degradation on bacterial cultures of Pseudomonas putida 54G were investigated in three reactor systems: a batch suspended culture system, a bench-scale flat plate biofilm reactor, and a bench-scale packed column reactor. Humidified air containing 150 ppmv (toluene limiting) to 750 ppmv (oxygen limiting) toluene vapor was the sole source of carbon and energy supplied to these systems. Results from the suspended batch culture experiments were used to develop rate expressions and kinetic parameters for loss of culturability and of toluene degradative capacity. Experiments in the flat plate reactor were carried out to examine the effects of injury on biofilm structure and function. The packed column studies were performed under conditions relevant to field application, and confirmed results from the other two studies - that decreased culturability on toluene media correlated with decreased specific toluene degradation rate, particularly at higher toluene concentration.