For the study of complex antigen structures, such as the adenovirus hexon capsomer, monoclonal antibodies proved to be very useful tools. Production and stabilization of monoclonal antibodies in a larger amount is complicated and requires special infrastructural background, if we apply the convential hybridoma techniques. Recombinant DNA and gene amplification technology, however, has made it possible to clone antibody genes in bacteria, and to produce antibodies in bacterial cultures.