Selenium supplements were not able to restore the ultrastructural changes in the myocardium of latent Keshan disease patients taken by using cardiac catheter endomyocardial biopsy. Observations on the changes of selenium status and the incidence of Keshan disease showed that new latent and naturally-occurring chronic cases were found in the endemic area even after selenium levels had been elevated in the residents to the levels typical in the non-endemic area. These results indicate that although selenium deficiency might be a primary pathogenetic geogen in the occurrence of Keshan disease, it is rather a conditional predisposing factor than a specific or initiative aetiologic factor for the occurrence of Keshan disease. Selenium supplementation could apparently alleviate the higher platelet responsiveness of residents in the endemic area, which might contribute to eliminating the basis for the occurrence of the multifocal perivascular necroses in myocardium of acute and subacute Keshan disease.