The anti-arsonate immune response of A/J mice is characterized by the occurrence of several recurrent idiotypes with a different temporal pattern of expression. The CRI-A idiotype is typically a memory idiotype since it appears late in the primary and dominates the secondary as well as subsequent immune responses. The CRI-C idiotype is present throughout the responses, including the primary one. Naive adult A/J mice treated repeatedly with anti-mu or anti-delta monoclonal antibodies exhibit a completely different balance of HSA(low) and HSA(high) B cell subsets and an opposite idiotype profile after immunization with p-azophenylarsonate coupled to hemocyanin. Anti-mu treatment leads to a striking enhancement of the HSA(low) cell subset associated with an earlier important synthesis of CRI-A(+) antibodies, while anti-delta treatment enhances significantly the HSA(high) compartment with a strong decrease of CRI-A and persistence of CRI-C1 antibodies. Semiquantitative PCR analysis reveals that the presence of CRI-A transcripts is associated with the HSA(low) compartment, while CRI-C transcripts are mainly associated with HSA(high) B cell subsets. This has been demonstrated with spleen cells of adult A/J mice treated with anti-mu or anti-delta antibodies and also with purified B cell subsets of unimmunized adult A/J mice and on neonatal spleen cells. It appears that the memory (CRI-A) idiotype is selected into the HSA(low) B cell subset before antigen arrival.