Very large 'naïve' human antibody repertoires have been obtained from RT-PCR cloned VH and VL variable regions. They are used as starting material for the assembly of medium sized combinatorial libraries or so called multicombinatorial libraries. In nonimmunized individuals immunoglobulin messenger RNAs are poorly expressed, which can be a serious limitation for cloning efficiency. To overcome this problem two complementary strategies have been used: a nonspecific polyclonal activation of B cells, and a secondary PCR amplification technique to ensure recovery of Ig messengers in large amount and without introducing any bias.