Enteroviral RNA in paraffin-embedded myocardial specimens from 21 patients with Keshan disease and 21 patients with cerebral trauma was investigated by nested polymerase chain reaction. Of the 21 patients with Keshan Disease, 18 (85.7%) showed positive findings. Their myocardial tissues were infected by enterovirus previously. The results suggest that enterovirus infection is the major cause of Keshan disease in the Chuxiong district, Yunnan province.