Polyacrylamide gel electrophoresis was used to compare protein profiles of members of the family Bacteriodacceae. Cell-free extracts were prepared and the protein components separated by multistage polyacrylamide gel electrophoresis. The profiles were distinct and reproducible thus allowing identification of species, subspecies, and minor strain differences. Lyophilization of the cell-free extracts did not alter the major protein components. The results indicate that the techniques used may be useful in conjunction with conventional tests in identification at the species level.