The possible involvement of nerves containing vasoactive intestinal polypeptide in Crohn's disease was investigated by immunocytochemistry and radioimmunoassay of specimens from 17 patients with well-defined clinical and histologic features of the disease. The characteristic pattern of slender fibers, evenly distributed across the gut wall, was seen in specimens taken from controls, which consisted of (a) specimens from uninvolved areas of gut from carcinoma resection (n = 17) and (b) jejunoileal specimens obtained during bypass operation for obesity (n = 8) as well as in four of the six specimens from patients with ulcerative colitis. In contrast, this characteristic pattern was lost in all 17 patients with Crohn's disease, the pattern being replaced by thickened and more intensely immunostained fibers. These changes were consistently found in the mucosa and submucosa, and in 13 of the Crohn's disease cases, the abnormal pattern was totally transmural, involving both the myenteric and submucous plexus as well as the muscle layers. There was a > 200% increase in VIP content, as determined by radioimmunoassay, in Crohn's disease (294 +/- 29 pmol/g wet wt, mean +/- SEM) in comparison with (a) ulcerative colitis (93 +/- 5 pmol/g [P < 0.001]), and (b) controls consisting of carcinoma resection (108 +/- 39) and bypassed gut from obese patients (86 +/- 27 [P < 0.001]). At least part of the previously documented autonomic nerve changes in Crohn's disease are, thus, due to an increase in vasoactive intestinal polypeptide innervation.