Clinical and experimental evidence indicates that ureterosigmoidostomy is associated with a high risk for the development of colonic cancer, while there is no reported evidence of increased risk in patients who undergo urinary diversion of other types. In the present study the histochemical and lectin binding characteristics of goblet cell mucin were investigated in biopsy specimens from patients who had undergone ureterosigmoidostomy and from patients who had undergone rectal bladder surgery. Specimens from transitional mucosa surrounding colonic cancers and from normal rectal mucosa were also studied. For histochemical studies the high iron diamine-Alcian blue method was used. FITC-conjugated Dolichus biflorus agglutinin (FITC-DBA) and Arachis hypogaea agglutinin (FITC-PNA) were used for the study of lectin binding characteristics. In contrast to the striking increase in numbers of sialomucin-containing goblet cells found in the patients who had undergone ureterosigmoidostomy, the mucin proved to be histochemically normal in the rectal bladder surgery group. Abnormal lectin binding patterns were observed in colorectal mucosa after urinary diversion of both types, with the abnormalities consisting of dramatic decreases in FITC-DBA labeling (compared with controls) and the appearance of substantial numbers of FITC-PNA-labeled goblet cells. These findings indicate that the pattern of mucin secretion is definitely abnormal in patients who have undergone urinary diversion. Whether this abnormality is an indicator of premalignant changes remains to be established. These data, however, confirm that endoscopic and histologic follow-up studies may be of value in assessing the risk for the development of cancer in these patients.