OBJECTIVE: Collagenous colitis (CC) is a chronic inflammatory bowel disease that affects the colon. However, some patients with CC present with accompanying pathologic small-bowel manifestations such as coeliac disease, defects in bile acid absorption and histopathologic changes in small-intestinal biopsies, indicating that CC is a pan-intestinal disease. In small-intestinal disease, the intestinal barrier function may be impaired, and the permeability of the small intestine altered. The purpose of this research was to study small-bowel function in patients with CC as expressed by intestinal permeability. MATERIAL AND METHODS: Ten patients with CC and chronic diarrhoea participated in the study. Coeliac disease was excluded by small-bowel biopsy and/or serology. Intestinal permeability was assessed as urinary excretion (ratios) 2, 4 and 6 h after ingestion of 14C-labelled mannitol (14C-mannitol) and 99mTc-labelled diethylenetriamine-pentaacetic acid (99mTc-DTPA). Data were compared with the results from healthy controls. RESULTS: No difference was found between groups in urinary excretion of 14C-mannitol and 99mTc-DTPA after 2, 4 or 6 h, respectively. Likewise, no significant differences in the 99mTc-DTPA/14C-mannitol ratios between patients and controls were detected after 2 h: 0.030 (0.008-0.130) versus 0.020 (0.007-0.030), p = 0.19, after 4 h: 0.040 (0.009-0.180) versus 0.020 (0.008-0.040), p = 0.14 or after 6 h: 0.040 (0.012-0.180) versus 0.020 (0.010-0.040), p = 0.17. CONCLUSIONS: No alterations in intestinal permeability in patients with CC could be demonstrated. Impairment of the integrity of the mucosa of the small bowel and the presence of a general dysfunction of the small intestine in patients with CC seem unlikely.