In individuals with varicella, complement-fixing antibody usually appeared in the serum 4 or 5 days after the development of the exanthem and further significant increases in titer were characteristically observed during the 2nd week of illness.

The complement-fixing antibody response in herpes zoster tended to follow the same pattern as in varicella, with the exception that in sera from some individuals relatively high titers were present in the acute phase specimen.

Complement-fixing antigens prepared from varicella strains or from a zoster strain reacted to essentially the same degree with convalescent sera from the homologous and the heterologous clinical entities. The varicella-zoster antigens did not fix complement in the presence of paired sera obtained from a limited number of individuals with primary infections due to herpes simplex virus or from individuals with generalized vaccinia infection.

Specific inhibition in vitro of the focal cytopathic process produced by the varicella-zoster viruses was demonstrated. This was accomplished by the incorporation of the sera under test as constituents of nutrient media of the cultures, either prior to or at the time of their inoculation with virus. The neutralization of focal cytopathogenicity thus obtained was relative in degree and never absolute; it was therefore assayed by repetitive counts of the number of focal lesions per culture in the various test groups.

Inhibition of varicella-zoster viral cytopathogenicity occurred in the presence of convalescent serum from either clinical entity.

The results of the immunologic studies with the viruses of herpes zoster and varicella as propagated in vitro are considered as providing further evidence in support of the concept of the close relationship and probable identity of the two agents.