For the purpose of evaluating the utility of CA19-9 determination in transitional cell cancer (TCC) of the urinary tract, its serum value, tissue level and, immunohistochemical study, and follow up study, with high serum value were examined in 43 cases with TCC and 13 cases of control. 1. Serum values were 19.1 U/ml in the control group and 198 U/ml in the tumor group. Though those of tumor were higher than those of the control group, there is no statistical difference between both groups. The cases with abnormally high value were observed in 13.7% of the control group, 13.8% of the bladder cancer, and 57.1% of the upper urinary tract cancer. 2. Tissue levels were 816 U/g wet tissue in the control group and 13,000 U/g wet tissue in the tumor group, showing a significantly higher value (p < 0.01) in the tumor group, statistically. 3. Immunohistochemical study were positive in 4.0% of the control group and 88.4% of the tumor group. 4. There is a significant correlation between serum values and tissue levels (p < 0.05, r = 0.483). 5. The serum values did not correlated with the staining property, tumor size, grade, and stage. 6. The tissue levels correlated with the tumor size, but did not correlate with the staining property, grade, and stage. 7. In the follow-up study of cases with high value, those, who had not attained postoperative normalization, died of recurrent carcinoma. In cases showing an elevation despite postoperative normalization, too, all showed recurrence. Only those, whose value were normalized and remained at the normal range, are living without metastasis.(ABSTRACT TRUNCATED AT 250 WORDS)