The spongiform encephalopathies may be caused by prions, infectious pathogens that differ from all other infectious agents in that they do not have deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). Very difficult to inactivate, they are composed of an abnormal protein. It is believed by many that prions cause sporatic and genetic neurodegenerative diseases, including scrapie and bovine spongiform encephalopathy in animals and kuru, fatal familial insomnia, Creutzfeldt-Jakob disease (CJD) and Gerstmann-Straussler-Scheinker disease in humans. Another, the new variant CJD in humans in England, is an example of a breech in the species barrier between humans and animals. Transmitted primarily via exposure to infected brain or spinal cord tissue or blood, there have been numerous iatrogenic cases from contaminated pituitary hormones, surgical equipment, dural grafts, corneal transplants and others. All facets of blood product manufacturing have been affected. Nurses should be aware of the latest developments, and able to practice infection control while providing the best patient/family information possible.