The transmissible spongiform encephalopathies (TSEs) (in both humans and animals) have been reviewed with the principal focus on bovine spongiform encephalopathy (BSE), its recent outbreak amongst cattle in the UK ('mad cow disease') and its sequelae. The possible reasons for this outbreak are discussed as well as a number of hypotheses reviewed for TSEs (e.g. prions, organophosphates, etc.) and current measures attendant with food safety and surveillance taken in the European Union. It is generally accepted that the combined weight of all the evidence to date supports the conclusion that the new rare but lethal variant Creutzfeldt-Jacob Disease (vCJD) is the human counterpart of the aetiological agent BSE and that eating meat from the infected animals is probably to blame for 24 deaths (23 in the UK and one in France) to date from vCJD. Considerable evidence from biochemical, immunologic, pathologic and genetic studies strongly suggests that PrpSC is the major component of the transmissible prion particle responsible for the rare fatal brain TSE diseases.