The histamine content of biopsy specimens obtained from patients with ulcerative colitis (UC), Crohn's disease (CD), or polyps was measured in vitro. This was done using colonic and rectal mucosa taken from affected and healthy tissue. In general, the results demonstrate a significantly higher histamine content in patients with UC. This was true with respect to colonic as well as rectal mucosa. Moreover, affected mucosa contained significantly more histamine than normal in UC and in CD. The histamine content of colonic and rectal mucosa was similar within each patient group. However, specimens from patients with UC again contained significantly more histamine than did those of patients with CD. The data underscore a distinct pathomechanism in UC and in CD. Therefore, determination of the histamine content of biopsy specimens may be an adjuvant criterion for the discrimination of different inflammatory bowel diseases.