A freeze-dried, formalized-erythrocytes-bound VZV antigen for indirect haemagglutination, VZV-HEM, was prepared. It was used to test serologically 46 children, all of them patients of Prague paediatric clinics, with a known history of chickenpox. For comparison, the same sera were tested by the indirect haemagglutination reaction with freshly prepared VZV antigen and by ELISA. All three serological tests gave congruent results in 97.8% of cases. The advantages of the VZV-HEM assay are results obtainable within 2 hours of serum dilution and simplicity. The assay is especially suitable for emergency testing the immunity of persons at risk.