Previous studies of age-related susceptibility to viral infection have focused largely on the effects of aging on the immune response. Little attention has been given to age-related changes in the infectivity of target cells. We show here a fourfold greater plating efficiency of herpes simplex virus type 1 (HSV-1) for cultured vascular smooth muscle cells derived from adult rats compared with cells from genetically identical pup rats. The difference in plating efficiency appeared to be due to differences in initial attachment of the virion to the cell surface. There were no differences in the rate of viral entry or the efficiency of viral replication at high multiplicities of infection and no resistant "subpopulation" of pup cells. The pup cells did not release a soluble inhibitor of infection. Infection in both cell types was inhibited similarly by basic fibroblast growth factor (bFGF). Although adult cells exhibited a more vigorous mitogenic response to bFGF than did pup cells, binding studies did not demonstrate significant differences in the binding of bFGF to the cell surface, suggesting that differential expression of high-affinity FGF receptors could not be correlated with the difference in infectivity. We speculate that differences in the distribution of heparan sulfate in the cell surface, which serves as the initial attachment site for HSV-1, may explain the observed differences in plating efficiency. Since age is a risk factor for the development of atherosclerosis, these results have potential implications for susceptibility of the vasculature to herpesviral infections as a function of the development of the vessel wall.