The bacterial community structure of phosphate removing activated sludge systems were compared. Samples were obtained from 21 different activated sludge systems, differing in design and phosphorus removal. Community structures were determined in a more direct manner by isolation of the total protein content of samples which alleviated the need to culture the bacteria. Proteins of the activated sludge samples were separated with SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The objectives of this study were: to compare the protein fingerprints of activated sludge systems which differ in design and P-removal. The results indicated little variation between the different zones. The specific sludge systems tended to cluster together indicating a specific community structure for each system. However, this did not influence the P-removing capacity of the different systems studied, indicating that the microbial community structure was not specific in terms of its P-removing ability.