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.