Interactions between the enteric nervous system and the immune system are suggested to play an important role in the pathophysiology of inflammatory bowel disease (IBD). This study aims to determine if chromogranin A (CgA), chromogranin B (CgB), and secretoneurin (SN) are detectable in feces (F) from patients with collagenous colitis (CC) and to compare the levels found in patients with ulcerative colitis (UC) and Crohn's disease (CD) before and during treatment. Patients with CC (n = 12) were studied before and after 3, 7, 28, and 56 days of treatment. Patients with IBD (UC, n = 21; CD, n = 11) were studied before and after 28 and 56 days of treatment. Clinical data were recorded, and fecal samples were collected at each occasion. F-CgA, F-CgB, and F-SN were measured by RIA. Eleven patients with CC, 21 with UC, and 10 with CD achieved remission. On inclusion, CC patients had higher levels of F-CgA, F-CgB, and F-SN than patients with IBD and controls. Patients with IBD expressed markedly lower levels of F-SN than controls. During treatment, F-SN in CC patients decreased to control levels but remained low in IBD patients. No change was found in F-CgA or F-CgB in any of the groups. In conclusion, CgA, CgB, and SN are detectable in feces, and CC patients express higher values than patients with IBD and controls. During treatment, F-SN decreased to control levels in CC. These findings suggest that the enteric nervous system is clearly involved in the pathophysiology of CC.