It is widely believed that Paget's disease of bone is due to a "slow virus" infection of osteoclasts with one of the paramyxovirus group. Controversy continues to surround the identity of the virus involved, however, since at different times evidence has been presented implicating measles virus (MV), respiratory syncytial virus (RSV), and canine distemper virus (CDV) as putative infective agents. In this study we used the technique of reverse transcription and polymerase chain reaction (PCR) to screen for paramyxovirus sequences in ribonucleic acid (RNA) extracted from pagetic bone. We were able to detect viral amplification products of the appropriate size in RNA extracted from as few as 50 cells experimentally infected with a wide range of paramyxoviruses, including measles, canine distemper, parainfluenza 3, and respiratory syncytial virus, but we found no evidence of viral products in RNA extracts of affected bone from 10 consecutive patients with Paget's disease. This study fails to support the hypothesis that active infection with one of these or a related paramyxovirus is involved in the pathogenesis of Paget's disease.