The epidermal growth factor receptor has been implicated in the malignant transformation of cells because the v-erbB oncogene is a truncated form of the epidermal growth factor receptor. DNA amplification and/or mRNA overexpression of the epidermal growth factor receptor is associated with the malignant potential of several human epithelial tumors. To determine the frequency of epidermal growth factor receptor DNA amplification and mRNA overexpression in bladder cancer, we evaluated 12 bladder tumors for DNA amplification and another 14 bladder tumors for mRNA overexpression. By Southern hybridization, we found no evidence of DNA amplification or gene rearrangements in 12 bladder tumors. Five of 14 bladder tumors overexpressed epidermal growth factor receptor mRNA four to 15 fold compared to normal urothelium from the same bladder by Northern analysis. These findings suggest that epidermal growth factor receptor amplification and/or gene rearrangement occurs infrequently in bladder cancer. Epidermal growth factor receptor mRNA overexpression, however, is found in 36% of bladder tumors and may play a role in bladder tumorogenesis.