C. difficile is known as the main cause of pseudomembranous colitis, however, some individuals may be asymptomatically colonized. In this paper two patients with diarrhoea had three respectively five negative stool cultures. Endoscopically, one patient had severe colitis consistent with both pseudomembranous colitis and inflammatory bowel disease. In the other case the endoscopic findings were typical for pseudomembranous colitis. In both cases there were positive cultures for C. difficile from biopsies from colon-plaques. We find that culture of biopsy of a colon-plaque may contribute to the detection of C. difficile infection in patients with negative stool cultures.