Apolipoprotein E (ApoE) plays a relevant role in herpes simplex type 1 (HSV-1) infection of the CNS; after infection by the hematogenous route, the viral neuroinvasiveness directly depends on the APOE gene dose. To analyze the effect of ApoE isoforms on the HSV-1 infectivity to the brain, we have used a model of hematogenous infection of mice humanized for the ApoE3 or the ApoE4 alleles, and we have analyzed the presence of viral DNA in several organs by real time quantitative PCR. We have found that animals expressing human ApoE4 present very high levels of virus in the brain when compared to those expressing the ApoE3 allele; in contrast, there were no significant differences in the viral levels found in peripheral organs. Apolipoprotein E4 seems to facilitate the entry and/or spread of HSV-1 in the brain much more efficiently than E3, pointing to a novel potential mechanism underlying the susceptibility to neurodegenerative processes associated with the ApoE4 allele.