This chapter reviews all proven or highly probable cases of environmentally acquired human spongiform encephalopathy (cannibalism, neurosurgical procedures, cornea1 and dura mater homografts, and natrve pituitary hormone therapy), and evaluates potential but as yet unverified environmental sources of disease, such as peripheral tissue homografts, organ transplants, administranon of blood, blood products, and other biologicals, occupational exposures, and zoonotic infections. Implicit in this breviary of known and putative origins of envtronmentally acquired disease are laboratory and epidemiologic methods for recognizing and if possible preventing subsequent cases both from present and future sources of infection.