A/He mice actively producing complementary or anti-idiotypic antibody directed against a combining site structure for phosphorylcholine (PC) have profound and long-lasting suppression of their response to PC. B cells from unresponsive mice are unresponsive in vitro, and attempts to demonstrate suppressor cells in unresponsive mice were unsuccessful. Although the process ultimately responsible for suppression has not been defined, suppression can be initiated by anti-idiotypic antibody alone and prevented by complementary Ig; i.e., by anti-PC antibody. Furthermore, a suppressed anti-PC response can be rescued by sublethal irradiation and anti-PC antibody given passively. The recovery of the suppressed response is slow and presumably results from maturation from "stem" cells, which are protected from tolerization by the passively given antibody. Thus, by extrapolation, one of the functions of secreted Ig may be to protect the clone that produces it.