The biopsy specimens of 91 patients between the ages of 38 and 94 with transitional cell carcinoma of the bladder were retrospectively reviewed to determine if the expression of CD15 antigen detected by a monoclonal antibody MC2 was correlated with prognosis. Expression was variable, ranging from strong expression of the antigen by only the superficial cells in well differentiated papillary lesions to weak expression by most cells in solid or invasive tumours. In the invasive component there was a correlation between MC2 expression and tumour type, suggesting that the cell surface carbohydrate detected by MC2 may have a role in cell adhesion. There was no correlation between staining and survival. It is concluded that tumour type, grade, and stage remain the best prognostic indicators of urothelial tumours.