Anti-idiotype antisera were obtained by immunizing allotype-matched rabbits with anti-p-azobenzenearsonate antibody (anti-ars) from an individual rabbit after each of four courses of immunization. These sera were used to study the relationship between anti-ars produced over a span of 33 months. Antibodies of limited heterogeneity produced 21 months apart had very similar idiotypes. Components with related idiotypes were also demonstrated to be present in the more heterogeneous earlier and later antibodies.