Clostridium difficile is now regarded as a major enteric pathogen in hospitals and nursing-home facilities. The pathophysiology of this pathogen involves alterations of the indigenous colonic flora by antibiotics, ingestion of spores and colonization by C. difficile, followed by release of its toxins. Although most of the research on the intestinal effects of C. difficile had been focused on its enterotoxin or toxin A, recent results indicate that toxin B, the cytotoxin of C. difficile, is also active in human colon. The cloning and sequencing of the toxin A and toxin B gene and the identification of the GTP-binding protein Rho as their intracellular target represent major advances in our understanding of the mode of action of these toxins. An important characteristic of C. difficile infection is the dramatic inflammation seen in pseudomembranous colitis. Recent studies indicate that an interplay between lamina propria neuroimmune cells and intestinal epithelial cells may be central in pathogenesis of this toxin-mediated inflammatory response.