Outer membrane protein (OMP) and lipopolysaccharide (LPS) phenotypic diversity among 27 oral and extraoral strains of Eikenella corrodens was assessed by SDS-PAGE. Each strain exhibited one to three major protein bands in the 35- to 41.5-kDa range and one or two protein bands of lesser density in the 24.5- to 28-kDa range. Eleven OMP patterns were distinguished among the strains. While oral strains obtained from periodontally healthy and diseased subjects exhibited diverse OMP patterns, five of six strains from extraoral sites of infection expressed an identical OMP pattern. Comparison of the electrophoretic mobilities of LPS from these same strains revealed that E. corrodens LPS consists primarily of low apparent molecular mass forms. Sixteen different LPS phenotypes were differentiated among the strains, with no apparent correlation between LPS phenotype and clinical setting. Strains expressing the same OMP pattern frequently expressed variable LPS phenotypes and vice versa. Analysis of OMP or LPS pattern by SDS-PAGE may be useful in taxonomic and epidemiologic studies of E. corrodens. Additional studies assessing the potential influence of OMP composition on invasiveness of this organism appear warranted.