Abstract
SUMMARY: An enzyme-linked immunosorbent assay (ELISA) was developed to detect IgG antibodies to diphtheria toxin in human serum. Serum samples obtained from 557 normal persons aged 1–65 years from different areas in New Zealand showed maximum antibody levels in the 1–9 years age group (95·1%) and the least in the 60–65 years age group (38·1%). The indirect ELISA is suitable for sero-epidemiological survey study as it is simple to perform, economical and precise.