Malignant pleural mesothelioma (MPM) continues to be a public health problem in Turkey, where exposure to environmental asbestos and fibrous zeolite (erionite) is the main cause of the disease. However, less than 5% of exposed individuals develop the disease, and numerous cases of MPM are documented each year in which the patient has no known exposure to either of these minerals. Thus, additional unknown factors act independently or as co-carcinogens in the development of MPM. Simian Virus 40 (SV40) may act as a co-carcinogen with asbestos in the pathogenesis of occupationally induced MPM. To determine if SV40 plays a role in the development of MPM in Turkey, we used PCR analysis to investigate if SV40 DNA sequences were present in 29 mesothelioma specimens from patients previously exposed to asbestos ol erionite. PCR analysis revealed that all 29 tissue specimens from our patients did not contain SV40 DNA. 15 specimens from patients suffering from tuberculosis pleuresy were also SV40 negative. One mesothelioma and one osteo-sarcoma fi om Italy feared positive for SV40. Out results indicate that inorganic fibers, asbestos, and erionite remain the only known causal factors of mesothelioma in Turkey. The absence of SV40 in Turkish specimens and its presence in Italian specimens may be related to the fact that SV40-contaminated vaccines were not administered in Turkey.