The place of inflammatory bowel disorders in the spondarthritis matrix has been discussed and aetiopathological and clinicoradiological features of their individual arthropathies described. Particular emphasis has been placed on the arthropathies of ulcerative colitis and Crohn's disease, but a comment is also included on the much rarer condition, Whipple's disease. The position of reactive arthritis resulting from enteric infection in relation to the spondarthritis concept is examined in the light of Reiter's-like clinical features and the association with HLA-B27. More 'peripheral' ideas of possible relevance to the spondarthritis idea (drug-induced colitis, intestinal-bypass syndrome) are included, together with a final section on experimental models of inflammatory bowel disease and of their arthropathies. It is concluded that certain inflammatory bowel disorders deserve a continuing place within the spondarthritis complex. Although their aetiopathogenesis is still imperfectly understood, it is likely that a blend of genes of small effect (polygenic inheritance) and environmental factors (e.g. microorganisms and/or their products) trigger disease processes which are enabled to manifest themselves by intermediary immunological processes. The precise way in which this is achieved is not yet known, but there is evidence that microorganisms (presumably in the gut of individuals genetically predisposed and suitably exposed environmentally) generate the formation of immune complexes. It is likely that these not only damage or further damage the mucosal lining of the bowel but also result in arthropathy and features of the disease 'distant' from bowel and joint (e.g. ocular inflammation, oral ulceration and skin manifestations). This concept is summarized in Figure 5.