Mucin glycoproteins form a viscoelastic gel which appears as a continuous protective barrier on the colonic mucosal surface. However, their structure and function in health and disease remain unclear. Further work is needed to define the structure of colonic mucin glycoproteins as well as the cellular basis for their heterogeneity. Further elucidation of the factors regulating their synthesis and secretion should provide insight into their function. A more detailed characterization of changes in mucin glycoproteins associated with specific disease processes may shed light on the role of these glycoproteins in the pathogenesis of a wide variety of colonic disorders.