Samples from laboratory-scale activated sludge systems operating under spesific conditions which differ in phosphate-removing capabilities were obtained from the University of Cape Town. The total protein content of samples of these systems was used and the protein separated with SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Analysis of the total proteins was employed as a fingerprint to type and compare the diversity of the bacterial communities of P-and N-removing systems. Samples of six activated slugde systems (three N-and P-removing and three N-removing) were used in this study. Protein profiles indicated a high (>70%) correlation for all the systems. No difference was observed in the protein profiles of the bacterial communities of N-and P-removing or N-removing systems. We can therefore conclude that the same bacterial communities were present in P-and N-removing systems.