Colonic tissue obtained at surgery from control individuals and patients with ulcerative colitis was used to isolate mucins and to prepare mucin glycopolypeptides by pronase digestion. These were compared with mucins labelled with [³⁵S] sulfate and [³H]-glucosamine after organ culture tissue samples from the same patients. A significant loss of mucin sulfation was detected in the colitis patients by both metabolic labelling and chemical analysis of the glycopolypeptides. A change in the size distribution of purified mucin oligosaccharides fractionated on BioGel P6 after release by β-elimination was seen in both radiolabelled and non-labelled colitis mucins compared with controls. Amino acid analysis of the glycopolypeptides showed a close similarity to the expected ratio of serine:threonine:proline for MUC2 and did not vary between control and colitis groups. Analysis of the mucins confirmed >90% purity in the labelling experiments, characteristic behaviour on density gradient centrifugation and agarose gel electrophoresis in control and ulcerative colitis groups and differences in sulfation and turnover at various sites in the normal colon.