The aim of this study was first to investigate the hypothesis that C. concisus mucosal biopsy isolates from different gastrointestinal disease phenotypes differ in pathogenicity by use of IL-8 production in HT-29 cells as a model for comparison; faecal, diarrhoeal isolates were also included in the study. This evidence concerns the gene CXCL8 and gastrointestinal disease.