Secondary antigen receptor gene recombination occurs in developing lymphocytes, and in more mature T and B cells. In the developing lymphocyte, "editing" occurs in response to receptor ligation by autoantigens. As a result of receptor editing, anti-self-reactive cells are converted to non-self-reactive cells, and self-reactive clones are thereby salvaged before negative selection. This antigen-induced change in the receptor specificity was not foreseen in the clonal selection theory. However, editing could be incorporated into the clonal selection theory by limiting receptor selection to a specific stage in lymphocyte development that precedes cellular selection as suggested by Jerne (1971). We know much less about the origin, regulation, or function of V(D)J recombination in mature lymphocytes. Nevertheless, antigen-induced receptor selection is likely to play an important role in shaping immune responses.