In Switzerland bovine spongiform encephalopathy (BSE) was detected for the first time in November 1990. It is a transmissible disease of the central nervous system similar to Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS) and kuru in man, and, in animals, scrapie in sheep and goats, chronic wasting disease (CWD) in captive mule deer and elk of North America and transmissible mink encephalopathy (TME) of farm reared mink. The infectious agent of the spongiform encephalopathies (SEs) is extremely small (greater than 100 microns) and very resistant against physical and chemical disinfectants. The infectiousness is closely linked to the so-called prion proteins, the biological and genetic properties of which are not yet fully understood. The first outbreak of BSE occurred in England, and the disease spread rapidly all over Great Britain. The source of infection proved to be bone and meat meal obtained from scrapie-infected slaughter wastes. So far we have diagnosed 17 cases of BSE in our country. The risk of humans contracting CJD by ingestion of meat, milk and their products contaminated with BSE is probably minimal.