AbstractMurine anti‐idiotypic serum against C3H.SW anti‐poly(LTyr, LGlu)‐poly(DLAla)–poly(LLys) [(T, G)‐A–L] antibodies was elicited in C57BL/6 mice. The effect of the anti‐idiotypes on the proliferation of primed lymph node cells was investigated. The anti‐idiotypic serum stimulated the proliferative response of the (T, G)‐A–L‐specific lymph node cells as well as of nylon wool‐enriched T cells. In the presence of suboptimal doses of (T, G)‐A–L, the addition of the anti‐idiotypes enhanced the proliferation to the levels obtained with the optimal dose of (T, G)‐A–L itself. These results suggest the existence of shared idiotypic determinants between antibodies and the (T, G)