The experimental host range for the slow virus infections causing subacute spongiform virus encephalopathies is enlarged in primates to include the gibbon for kuru, the pigtailed macaque for Creutzfeldt-Jakob disease, and the sooty mangabey for both diseases. The report is based on neuropathological evidence of the diseases in animals with preclinical lesions. A table lists all the species to which the subacute spongiform virus encephalopathies have been transmitted.