To investigate the molecular basis for measles virus persistence in patients with subacute sclerosing panencephalitis (SSPE), the authors used a high-density oligonucleotide microarray, and found that the expression of granulysin in peripheral blood mononuclear cells was significantly lower in the patients than in the controls. By a quantitative reverse transcriptase-polymerase chain reaction, the mRNA levels of granulysin were decreased in 30 SSPE patients, and were increased in 7 measles patients, as compared to the 23 controls. These results imply that granulysin might play a role in the host defense against measles virus and possibly be involved in the pathogenesis or pathophysiology of SSPE.