EF (E. Falsen) group 22, a group of Campylobacter strains sorted out by routine immunotyping among unidentified or misidentified human nonoral clinical specimens, was characterized by numerical analysis of gel electrophoretic protein profiles and immunotyping. The protein electrophoretic and immunotyping analyses, DNA:DNA hybridizations, and the DNA base composition demonstrated unambiguously that all EF group 22 strains belong to Campylobacter concisus. EF group 22 strains have DNA binding values of at least 42% with the type strain of C. concisus, showing a considerable degree of genomic heterogeneity. The isolation from blood, esophagus, stomach, duodenum, and feces of humans in association with different gastrointestinal disorders considerably extends the clinical significance of this species. Our results indicate that sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunotyping are excellent tools for the identification of the fastidious C. concisus strains and relatives.