Eighty-two patients were investigated on their first visit to the outpatient department of St. Mark's Hospital, London, for the assessment of abdominal symptoms. In addition to the clinical examination, a rectal biopsy, routine tests and appropriate special investigations, blood was taken from each patient for the determination of erythrocyte sedimentation rate, C-reactive protein and alpha-1-acid glycoprotein. Nineteen patients were finally diagnosed as having Crohn's disease, twenty-two ulcerative colitis, and forty-one functional bowel disorders. All the patients with Crohn's disease had an elevated erythrocyte sedimentation rate and C-reactive protein level as had 11 (50%) of the patients with ulcerative colitis, but none with functional disorders. All cases of ulcerative colitis could be diagnosed by rectal biopsy. Measurement of alpha-1-acid glycoprotein provided no additional diagnostic information. A combination of rectal biopsy, and measurement of the erythrocyte sedimentation rate and C-reactive protein successfully distinguishes between inflammatory disease of the large and small bowel and functional bowel syndrome.