The production of high-affinity monoclonal antibodies (mABs) is generally restricted to antigens recognised as foreign by the immune system. Here we report the generation of mouse mABs specific for mouse IgD. Mice rendered IgD-deficient by gene targeting and consequently immunologically fully responsive to mouse IgD, were used to elicit a humoral response against mouse IgD. Hybridomas producing mABs of high affinity were isolated and clones specific for non-allotypic determinants on the Fc or Fab portion of mouse IgD were obtained. The data show that mice lacking a protein of interest due to targeted gene inactivation can be utilised for the production of high-affinity mABs specific for that mouse protein and should also facilitate the generation of mABs specific for proteins highly conserved between species.