The development of an ELISA of increased sensitivity has permitted a more critical evaluation of human humoral immune responses to the live attenuated varicella (Oka/Merck) vaccine. For use as a solid-phase antigen, the glycoprotein (gp) antigens are prepared by lectin-affinity chromatography from lysates of VZV-infected MRC-5 cells. The lot-to-lot variation in VZV gp content is controlled by standardization of antigen against a panel of human serum providing antigen-coated plates of consistent quality. The increased sensitivity of the gpELISA over the VAR ELISA is reflected in the greater seroconversion rate and prepositive rate specificity. These determinations have been shown to be specific for anti-VZV by absorption experiments using purified VZV gp antigens.