The influence of maternally transmitted immunoglobulins on the development of autoimmune diabetes mellitus in genetically susceptible human progeny remains unknown. Given the presence of islet β cell–reactive autoantibodies in prediabetic nonobese diabetic (NOD) mice^,, we abrogated the maternal transmission of such antibodies in order to assess their influence on the susceptibility of progeny to diabetes. First, we used B cell–deficient NOD mothers to eliminate the transmission of maternal immunoglobulins. In a complementary approach, we used immunoglobulin transgenic NOD mothers to exclude autoreactive specificities from the maternal B-cell repertoire. Finally, we implanted NOD embryos in pseudopregnant mothers of a non-autoimmune strain. The NOD progeny in all three groups were protected from spontaneous diabetes. These findings demonstrate that the maternal transmission of antibodies is a critical environmental parameter influencing the ontogeny of T cell-mediated destruction of islet β cells in NOD mice. It will be important to definitively determine whether the transmission of maternal autoantibodies in humans^,,,, affects diabetes progression in susceptible offspring.