Mesothelioma is an aggressive tumor arising from the mesothelium, and is usually associated with previous exposure to asbestos. The incubation period of the tumor may be described as 30-40 years, and the prognosis is dismal. We previously discovered the Erc (Expressed in renal carcinoma) gene in the Eker rat model (Tsc2 gene mutant) and it was a homolog of the human mesothelin/MPF gene. We developed a novel ELISA system (N-ERC/mesothelin). Recently, we found that N-ERC/mesothelin was a potentially useful diagnostic marker for asbestos-related mesothelioma.