Crude cell walls of Staphylococcus aureus of potential immunologic or epidemiologic importance were prepared for study by mechanically disrupting whole cells and applying differential centrifugation. Cell-wall proteins were then released from the wall by lysostaphin digestion and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Distinct electrophoretic protein patterns were found for each of the 12 serologically distinct strains examined. There were two major groups of cell-wall proteins identified in the 45-57-kilodalton (kdal) and 100-190-kdal range, respectively. Proteins in the 45-57-kdal range appeared to represent protein A variants of different apparent molecular mass. Localization experiments with 125I labeling demonstrated the surface location of most of the proteins. These data suggest that selected surface-exposed proteins may be important in defining host immune responses to S. aureus infections.