naive antibody libraries have been more generally used. These are built from diverse lymphoid source, including peripheral blood, bone marrows, and thus harvest naturally assembled binding sites. To minimize biases of the libraries, owing to the inclusion of v-genes of unrelated immune response in the donor, the B cells can be enriched for IgM-IgD surface expression, or the variable heavy-chain genes can be amplified from IgM mRNA. Provided the repertoire constructed is diverse, larger libraries give rise both to many more different antibodies against a given antigen, and also to higher affinity antibodies site. As a consequence, there have been several efforts to establish vary large primary libraries.