Tumor-associated glycoprotein 72 (TAG-72) is a large, high molecular weight, mucinlike antigen that is expressed in a wide variety of human carcinomas. Three different TAG-72 monoclonal antibodies (MAbs), designated B72.3, CC49, and CC83, were applied to the following archived samples from the dog: 1) 51 transitional cell carcinomas of the urinary bladder, 2) 15 hyperplastic/inflamed urinary bladders, and 3) eight normal urinary bladders. Immunoreactivity was detected with an avidin-biotin complex immunoperoxidase method. Fifty-three percent (27/51) of transitional cell carcinomas were positive (> or = 5% staining) for MAb B72.3. MAb B72.3 staining of these transitional cell carcinomas did not statistically correlate with any of the examined features of malignancy, including histologic grade, clinical stage, DNA ploidy, or presence of vascular/lymphatic invasion. In regard to the staining of transitional cell carcinoma by the other two TAG-72 antibodies, 53% (27/51) of the samples were positive for MAb CC83 and 63% (32/51) were positive for MAb CC49. The finding that similar populations of neoplastic urothelial cells in serial sections from the same neoplasm stained with all three TAG-72 antibodies supports the hypothesis that an antigen similar to TAG-72 was expressed in canine transitional cell carcinoma. None of the normal urinary bladders nor any of the hyperplastic/inflamed urinary bladders stained with any of the three TAG-72 antibodies tested. The results of these studies demonstrated that the staining of canine transitional cell carcinoma with all three TAG-72 antibodies was specific for neoplastic urothelial cells and that an antigen similar to TAG-72 was expressed.