Prion gene sequence is thought to affect the phenotypic expression of prion disease and the E2 variant of apolipoprotein E (Apo E) can be neuroprotective in dementia. We determined codon 129 of the prion gene and the Apo E variants in Creutzfeldt-Jakob disease (CJD) using PCR and restriction digest. We found a significant correlation between valine at codon 129 of the prion protein gene and the presence of plaque in CJD and a later age of onset in CJD cases possessing the Apo E2 allele. This study provides further evidence that sequence variations in the prion gene can modify disease pathology and the neuroprotection afforded by Apo E2 is not confined to Alzheimer's disease.