Abstract
Seventy polio virus strains, identified as single types by their reactions in the neutralization test, were studied in the complement-fixation reaction. For each strain an antigen was prepared in monkey kidney culture and this was tested against 3 standardized sera, each representing a different type. About 1/2 of the newly isolated strains were found to be ditypic and showed Type I and 2, or Type 2 and 3, antigens. A few strains were tritypic. The major antigen identified in the complement-fixation test agreed with the type assigned to the strain from its reaction in the neutralization test. The findings may help to explain the heterotypic antibody response in poliomyelitis infection of man, and the epidemiological correlations between the prevalence of Type 2 antibodies and immunity to Type 1 or Type 3 strains.