The ability of varicella zoster virus (VZV) to infect and replicate in human keratinocytes in culture was examined. Primary human keratinocytes derived from the abdomen, breast, and foreskin were plated as monolayers and infected by co-cultivation with VZV infected fibroblasts (MRC-5 cells). Replication and spread of the virus was assayed by plaque assay and immunofluorescence of infected cells using a VZV specific monoclonal antibody. Although all three types of keratinocytes tested were capable of supporting productive VZV infection, the keratinocytes showed a 1.5 to 2 log reduction in virus yield as compared to infection of monolayer cultures of MRC-5 cells. Results from immunofluorescence studies and plaque assays indicate a slower rate of cell-to-cell spread of the virus. Testing of an anti-VZV compound in this novel assay system demonstrated an interesting sensitivity compared to that observed in conventional assay systems.