The influence of structural variation, previously observed in a panel of V186.2 VH/V lambda 1‐expressing anti‐NP antibodies from the secondary response, on the affinity of these antibodies was examined by site‐specific mutagenesis and recombinant antibody construction. A tryptophan––leucine exchange at position 33 in the VH segment of all but one of the high‐affinity antibodies is the most frequently observed somatic mutation and by itself leads to a 10‐fold higher affinity; all other somatic exchanges are irrelevant for affinity selection. In the single case of a high‐affinity antibody without this common exchange, high affinity is mediated by a combination of mutations (including a one‐codon deletion) in VH and the particular D‐JH rearrangement carried by this antibody. The data indicate that the pattern of somatic diversification through hypermutation is shaped by affinity selection, but that only a single point mutation is available in the VH and the VL gene of lambda 1 chain‐bearing anti‐NP antibodies which by itself leads to an increase of hapten‐binding affinity. Based on the analysis of two secondary response antibodies from which somatic mutations in VH and VL have been eliminated, it is also concluded that the recruitment of B cell clones into the pathway of hypermutation involves a mechanism which is not based upon affinity differences towards the antigen.