AbstractA requirement for idiotype matching was reported such that carrier‐primed T helper cells from mice, which are unable to produce an idiotype (idiotype‐negative) because of genetic reasons or adult anti‐idiotype or neonatal anti‐μ antibody treatment, did not provide helper function for an idiotype‐positive antibody response.We have analyzed the requirement for idiotype matching in the response to phosphorylcholine by using mice which are idiotype‐negative because they were injected with anti‐idiotype antibody shortly after birth. Carrier‐primed T cells from such animals supported idiotype‐positive responses when mixed with normal or primed B cell populations and challenged with appropriate antigen; these responses were quantitatively and qualitatively similar to those obtained with T cells from idiotype‐positive animals. These results demonstrate no requirement for idiotype matching and suggest that the procedure used to establish an idiotype‐negative T cell donor may be decisive in showing a requirement