Abstract Idiotope-specific immunoenhancement or suppression was induced in C57BL/6 mice by the injection of physiological amounts (100 ng-10 μg) of monoclonal anti-idiotope antibody. As previously described, nanogram doses enhanced idiotope expression while a 10-μg dose of anti-idiotope antibody induced the activation of a population of Thy 1.2 +, Lyt 1 −, 2 + suppressors. Both positive and negative regulatory activities were confined to the non-μ, idiotope + compartment of the plaque-forming cell response. Administration of intermediate doses of anti-idiotope antibody resulted in an immune state indistinguishable from that of naive mice. This apparently normal response was in fact the product of a simultaneous activation of balanced enhancing and suppressive activities. When treated with anti-Lyt 2 or -Lyt 1 and complement, spleen cell populations taken from such phenotypically “naive” mice revealed latent idiotope-specific immunoenhancement or suppression, demonstrating the components of a functional regulatory equilibrium.