There is indirect evidence that various viruses have aetiological roles in the idiopathic inflammatory myopathies. By means of a sensitive and specific method based on the polymerase chain reaction (PCR), we sought direct evidence for the presence in affected muscle of nucleic acid sequences from Coxsackie virus, mumps virus, encephalomyocarditis virus, adenovirus, human T-lymphotropic virus types I and II, and human immunodeficiency virus. RNA was extracted from muscle biopsy samples obtained from 44 patients with idiopathic inflammatory myopathies a mean of 45 (range 0-216) months after disease onset. All the subjects were older than 16 years at disease onset. The integrity of the mRNA extracted was confirmed by the successful PCR amplification of insulin receptor mRNA in all samples. The PCR method was able to detect between 1 and 20 molecules of added viral nucleic acid for the picornaviruses sought. No detectable virus sequences were found, however, in any of the patients' muscle samples or in samples from 13 controls. We tested for retroviral DNA in 22 samples (17 patients, 5 controls) that met our criterion for adequate DNA extraction (detectable beta-actin DNA by PCR); again no virus sequences were found. Persistence in muscle of these or closely related viruses is unlikely to be a continuing stimulus for disease in the idiopathic inflammatory myopathies.