Intestinal permeability was measured using a low molecular weight polyethylene glycol as a permeability marker in patients with osteoarthritis, ankylosing spondylitis (AS) and rheumatoid arthritis (RA). Patients with AS showed a significant increase in bowel permeability when compared to controls. Intestinal permeability was also increased in patients with active RA but was less than the control group in RA patients who did not have active joint disease.