A method for testing serum tetanus immunoglobulin (TIG) was set up using enzyme immunoassay kit (EIA kit) and prepared by competitive principle in this laboratory. Forty-eight human sera tested by both EIA and toxin neutralization test (NT) in mice were in good agreement. Determination coefficient (r2) of the EIA and NT was 0.922. The lowest detectable dose was 0.1 IU/mL ELISA value. Many authors believe this ELISA value to be a safe protection TIG level. For serological survey of immune response to tetanus toxoid, sera from two groups of subjects were examined. Among 83 subjects, each over 40 years of age, only 47.0% were positive to TIG EIA level. Forty-six subjects with undetectable EIA titres to tetanus toxoid (TT) were immunized against two doses of TT at an interval of four weeks; 44 (95.6%) demonstrated TIG concentration of greater than or equal to 0.2 IU/mL within two weeks to one month following the last dose vaccination. The TIG positive rates of 725 school students' sera, selected by multistage sampling from 2395 specimens, were reported. Those were collected by simple random sampling from geographical area in the North, South, Central, Central Mountain, and East areas of Taiwan according to age groups. They were 80.8%, 65.1%, 56.0%, and 42.0% to the age groups of 0-4, 5-9, 10-14, and 15-17 years respectively. The probabilities of each near by two groups were p less than 0.1; p less than 0.05; p less than 0.05. The differences of positive rates in the last three groups were significant.