Varicella-zoster virus, a reclusive alpha-herpesvirus, can be isolated and propagated in a limited number of human cell lines. Under in vitro conditions, the virus is strongly cell-associated and, therefore, difficult to recover in a truly cell-free state. The general replication cycle includes the three phases called immediate early, early, and late. An example of an early viral protein is a putative protein kinase called open reading frame (ORF) 47. An example of a late protein is the preponderant viral glycoprotein (ORF 68) designated VZV gpI.