Variant Creutzfeldt-Jakob disease (vCJD) is a novel human prion disease caused by the bovine spongiform encephalopathy agent. Most cases have occurred in the UK, with smaller numbers in 11 other countries. All definite vCJD cases have occurred in methionine homozygotes at codon 129 in the prion protein gene. Following oral infection, the vCJD agent appears to replicate in lymphoid tissues during the asymptomatic phase of the incubation period. At present, four probable cases of vCJD infection have been identified following transfusion of red blood cells from asymptomatic donors who subsequently died from vCJD. Recently, one case of likely transmission of vCJD infection by UK Factor VIII concentrates has been reported in an elderly haemophilic patient in the UK. The recent report of a blood test that may be used to detect vCJD has raised the possibility of a new way to identify infected individuals, perhaps even before the onset of clinical symptoms.