Abstract
CBA/J females mated with DBA/2 display a high level of fetal wastage which can be corrected by anti-Balb/c vaccination. A batch of CBA/J anti-(CBA/J anti-Balb/c) antiserum was raised. This serum was characterized as anti-idiotypic by various techniques, including a solid-phase radioimmunoassay. Such a serum proved to confer protection against resorbtions when injected into CBA/J mice mated with DBA/2. However, the kinetics of the effect pointed to the need for administration in early pregnancy for successful protection. The significance of these data, and the possible mechanism(s) by which the serum acts, are discussed.