During the period between December 1970/ December 1971, a group consisting of 3,464 migrants, in transit, through São Paulo (Brazil) was placed under observation in order to classify them in relation to the demographic and social conditions and, more specifically, to determine tetanus antibody levels in sera by Passive Haemagglutination Technique. In selected sera, with different tetanus antibody levels by Passive Haemagglutination Technique, tetanus antibody level — were correlated with "in vivo" Neutralization Method. The correlation between "in vitro" and "in vivo" results, indicated of Passive Haemagglutination Technique showed a low predictive values (47%), but the simplicity of the technique, the high sensitivity and the low cust make it suitable for large scale soroepidemiological surveys. The data collected of negative tetanus antibody levels in 55% of the studied group, associated a low protective tetanus antitoxin in 1% total population and 0.3% of 15-44 years women group, explain in this low social class group our high tetanus morbidity and mortality.