Objectives-A persistent infection of enteroviruses and cardioviruses has been implicated in polymyositis and dermatomyositis, but conventional hybridisation studies ofthe presence of enterovirus RNA and encaphalomyocarditis (EMC) virus RNA in affected muscle have yielded conflicting results. To investigate further the possibility of viral persistence, the presence of viral RNA in muscle from patients with adult onset polymyositis and dermatomyositis was investigated using a polymerase chain reaction (PCR) technique.