The concentration of carcinoembryonic antigen (CEA) in urine and serum was determined repeatedly during one year in 213 patients followed because of previously treated urothelial carcinoma of the bladder. The findings were correlated to grade and stage of previously treated tumour, given therapy, recurrence and the cytological evaluation of a midstream urine specimen. During the period of follow up 43 recurrences were clinically observed. With the exception for the content of inflammatory cells no correlation was found between the CEA levels in urine or blood and the parameters studied. Thus CEA in urine and/or serum cannot substitute for cystourethroscopy, urography and exfoliative cytology in the follow-up of patients previously treated for urothelial carcinoma.