It has been reported that DNA of SV40, a virus of Asian macaques that is tumorigenic for rodents and can transform human cells in vitro, is present in pleural mesotheliomas and in several other cancers. To verify these observations, we tested paraffin sections from mesothelioma tissues of 50 patients for SV40 DNA using PCR with two separate sets of primers. The analytic sensitivity for detection of SV40 DNA was 1-10 genome copies. We also tested the specimens for beta-globin by PCR to assess the suitability of the specimen DNAs for amplification. beta-Globin amplification was detected in 48 of the 50 specimens, but SV40 DNA was not detected in any tumors, with either of two SV40 primer sets. Furthermore, sera from 34 additional patients with mesothelioma, 33 patients with osteosarcoma (another cancer reported to be SV40-related) and 35 controls were tested for SV40 antibodies by a plaque neutralization assay. The serological data, like the DNA results, did not support an association of SV40 with mesothelioma or with osteosarcoma; antibodies to SV40 were detected in three mesothelioma patients, in one osteosarcoma patient, and in one control. These findings call into question the association of SV40 with mesothelioma.