To study the possible role of viral infection in the etiology of subacute 
thyroiditis (SAT), we measured serum virus-specific antibodies to measles, 
rubella, mumps, type I herpes, chicken pox, human parvovirus B19 and 
cytomegalovirus (CMV) in 10 patients with SAT during the course of illness. In 
spite of the presence of IgG to each virus in more than 70% of patients, no 
significant changes in the IgG titers were observed except those to measles, 
rubella, chicken pox or CMV in only 10% of patients, respectively. Then we 
examined the presence of virus DNA in specimens of 9 patients with SAT obtained 
by fine-needle aspiration biopsy (FNAB) of the thyroid. DNA was amplified to 
detect that of Epstein-Barr virus and CMV by polymerase chain reaction. However, 
none of them were detected in all the specimens. Whereas previous studies 
suggest the involvement of viral infection in the pathogenesis of SAT, we failed 
to demonstrate significant changes in serum antiviral antibody titers or to 
detect viral DNA in the specimens obtained by FNAB of the thyroid. Thus further 
studies are clearly required to establish the definite role of viral infection 
in the pathogenesis of SAT.