Expression of the c-erbB-2 gene product and the epidermal growth factor receptor (EGF-R) was investigated in 54 cases of human bladder cancer immunohistologically and by Western blot analysis. For detection of the c-erbB-2 product, two specific antibodies, a rabbit polyclonal antibody directed to the intracellular domain and a murine monoclonal antibody recognizing an epitope in the extracellular domain, were used. Seventeen cases of bladder cancer were stained by the anti-c-erbB-2 polyclonal antibody, while 20 cases were stained by the monoclonal antibody, with good correlation on both stainings (p less than 0.01). There were four c-erbB-2 positive cases in 26 G1 tumors, four in 15 G2 tumors, and nine in 13 G3 tumors. There were also eight erbB-2 positive cases in nine muscle-invasive tumors, nine of 45 superficial tumors, four of five with lymph node metastasis, and seven of 14 without metastasis, as revealed by staining with the polyclonal antibody. Thus, the c-erbB-2 gene product was more frequently expressed in high grade tumors (p less than 0.01), in high stage tumors (p less than 0.01), and nodal metastatic tumors (N.S. by Chi-square test). Twenty-two of the 54 tumors were stained by an anti-EGF-R monoclonal antibody, 528 IgG. The expression of EGF-R was independent of histological grading, tumor stage, and nodal status, and no correlation was observed between expression of the c-erbB-2 product and EGF-R. The c-erbB-2 product may be applicable as a tumor marker for evaluation of malignant potential, invasiveness, and probably metastatic potential of human bladder cancer.