The whole-cell protein-profiling technique was evaluated for identifying Enterococcus species. Reference strains, strains from human infections, from animals other than human, and from environmental sources were studied. Whole-cell extracts were obtained by lysozyme treatment and were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and densitometry. Each Enterococcus species had a unique and distinguishable whole-cell protein profile. The major differences among species-specific profiles were found in the positions corresponding to 60-40 and 30-20 kDa. Profiles of the same species did not show qualitative variations. Analysis of whole-cell protein profiles was shown to be a relatively simple, easy, and reproducible procedure for the reliable and fast differentiation and identification of the enterococcal species.