Complement-fixing antibodies are confined to the age of 1 to 9 years if a serum dilution of 1:4 is used in the test, or to the age of 1 to 4 years with a serum dilution of 1:16.

A comparison has been made of the findings obtained in this study with the results for neutralizing antibodies previously reported. Complement-fixing antibodies were found to be temporary in nature while neutralizing antibodies were maintained for long periods of time. On this basis, criteria for "recent," "old," or "no infection" in poliomyelitis have been established.

Sixteen of the children were bled again in 1952, 18 months after the first bleeding and both series of sera were compared in complement fixation and neutralization tests. All children who were negative in 1950 and who developed c-f antibodies by 1952, also developed neutralizing antibodies to a titer of more than 1:250 during the same period. Some children who failed to develop c-f antibodies, did develop neutralizing antibodies although of lower titer than found in children in whom c-f antibodies made their appearance.

These findings are discussed in the light of theories regarding the mode of acquisition of antibodies to poliomyelitis virus.