The occurrence and/or deletion of A, B, H isoantigens in cytologic specimens was compared to a number of other clinical parameters commonly used for prediction of prognosis or monitoring of bladder carcinoma. Isoantigens were better preserved by our preparation for cytologic than for histologic specimens. Patients with isoantigen present on urothelial cells were more likely to have small or no visible tumors than large tumors. A strong correlation was found between isoantigen status and cytologic diagnosis (P less than 0.001), but not with ploidy (P = 0.059). For short-term prognosis of recurrence, tumor size appeared to be highly significant, whereas A, B, H isoantigen determinations had no predictive value. Intravesical chemotherapy did not per se influence expression/deletion of isoantigens.