The purpose of the study was to determine if the Biolog identification system could be adapted to detect physiological changes in the composite microbial community of activated sludge in an industrial wastewater treatment system. The detected temporal changes were correlated with other microbial characterization methods. Composite community samples were tested over time using Biolog titre plates. The results of the communities were compared with each other to 1) obtain an index of similarity with regard to their ability and inability to utilize the 95 substrates that are a part of the Biolog profile, and 2) ascertain shifts in the overall physiological capabilities of the community for the strict utilization of the 95 substrates. The results suggest that the Biolog identification system can be used to detect changes in the activated sludge microbial community. Other indices of community structure support the Biolog indications of community change.