Results with a VZV skin test as a marker of past infection were compared with histories of chicken pox and specific antibody detected by ELISA in 100 individuals—25 of whom were pediatric patients with malignant diseases. A negative or uncertain history was not reliable, neither were the skin test results among the oncology patients. However, among the normal individuals, the skin test when compared with the ELISA had a sensitivity of 85%, a specificity of 100%, and a positive predictive value of 100%.