The evaluation of the poliomyelitis vaccine field trials conducted in the USA in 1954 showed that there was considerable variation in the antigenicity of the vaccines then in use. Since then, however, there have been changes both in manufacturing procedures and in immunization schedules; and a new study has therefore been conducted into the antibody response of triply negative children, aged 6months to 3 years, to commercial vaccine. The results show good response for all three poliovirus types after three injections. After two doses antibody levels were relatively low, but the rise in level after the third dose was substantial and resulted in aggregate conversion rates of over 80% for all three types at a serum dilution of >/= 1:4. The limited data available indicate that the correlation between animal tests and the results in man is low but sufficient to make it possible to rate vaccines as "good" or "poor". There was no demonstrable influence of geographical location on antibody response.