Although most lung carcinomas and mesotheliomas are associated with well-known risk factors, these cancers develop in only a minority of persons exposed to known risk factors. On the other hand, these cancers develop in some patients without exposure to known risk factors. This indicates that other environmental factors play a role in the carcinogenesis of these tumors. Oncogenic viruses such as Epstein-Barr virus (EBC) are well-established agents in the development of certain cancers. EBV genomes have been detected by in situ hybridization in gastric adenocarcinomas and in nasopharyngeal carcinomas. To determine whether EBV infection is associated with pulmonary adenocarcinoma or mesothelioma, we performed EBV-encoded RNA-1 in situ hybridization on 80 pulmonary adenocarcinoma and 50 mesothelioma resection specimens. Sections were cut from paraffin-embedded tissue and EBV-encoded RNA-1 in situ hybridization was performed using an antisense oligoprobe. Sections were reviewed for the presence of EBV-encoded RNA-1 in tumor cells. All 80 adenocarcinomas and 50 mesotheliomas were negative for EBV-encoded RNA-1 by in situ hybridization. In conclusion, no evidence for an etiologic role for EBV in the development of pulmonary adenocarcinoma or pleural mesothelioma was found in this study.