It is well known that immunoglobulins with no identifiable immunogenic origin, called natural antibodies, are present in the sera of healthy individuals and their role as a defence against important pathogens has been proposed. Unfortunately, the studies are hampered by the fact that these immunoglobulins seem to have low affinity and to be polyreactive, and are commonly available in polyclonal preparations. Lately, new technologies for the production of monoclonal antibodies became available, and in particular the cloning of genes coding for antibody fragments in combinatorial phage display vectors provided a handy tool for the selection of human monoclonal antibodies. In this work, we describe the successful development of a technology for the molecular cloning of combinatorial phage display libraries containing genes coding exclusively for antibody fragment of the IgM or IgD phenotype. These libraries can be useful for molecular cloning of monoclonal antibodies of the IgM and IgD phenotype and can help elucidate the role played by natural antibodies in defence against infectious agents.