If crossreacting antibodies between varicella-zoster virus (VZV) and herpes simplex virus (HSV) exist, one would expect more positive reactions with VZV in a group of HSV positive patients than in a group of HSV negative patients. This statement can only apply to a group of individuals where positive and negative reactions with respect to HSV and VZV are evenly distributed. Such a distribution can only be found among children. Therefore, the relationship between HSV-1 and VZV was the only one which was considered in this investigation, since the incidence of HSV-2 antibodies in children is very rare. The sera from 197 children were examined using the neutralization test (NT), the complement fixation test (CFT) and the indirect immunofluorescent assay (IFT) and could be classified as either HSV positive (80) or HSV negative (117). The children's ages were similar in both groups. Approximately the same proportion of VZV positive sera was found in both groups when examined using IFT (53% in the HSV positive and 47% in the HSV negative group). However, when the CFT was applied the proportion of VZV positive sera in the two groups differed markedly (22% of the HSV positive sera and 38% of the HSV negative sera). These findings suggest that crossreactivity observed between HSV and VZV in acute HSV and VZV infections is evidently not dependent on crossreacting antibodies but is apparently confined to the cellular level of the immune response.