Gut permeability as measured by the 51Cr-EDTA resorption test was determined in 56 patients with rheumatoid arthritis (RA), 73 patients with spondyloarthropathies (SpA), 18 patients with inflammatory bowel disease (IBD) and 97 controls (42 patients with no inflammatory rheumatic diseases and 55 healthy controls). Gut permeability was found to be increased in the 3 patient groups, partially due to the intake of antiinflammatory drugs. When only patients not taking these drugs were considered, an increased gut permeability was found in patients with SpA and IBD. In patients with RA gut permeability could not be evaluated as they were all taking antiinflammatory medication. Ileocolonoscopy with biopsies of the gut was performed in 62 of the 73 patients with SpA and disclosed subclinical gut inflammation in 21. No difference in gut permeability was found between patients with or without gut inflammation. However, when the type of gut inflammation was considered, a significant increase of gut permeability was found in patients with chronic gut inflammation compared with patients presenting acute lesions. Our findings again suggest that the chronic gut inflammation seen in SpA is fundamentally different from acute gut inflammation and possibly related to the gut inflammation of IBD.