Phage antibody library selections on peptides or proteins are usually carried out using antigens directly coated on a plastic surface (e.g. Petri dishes, microtiter plate well, immunotubes, Chapter 9). This straightforward method is easy to perform and has been shown to be very successful for a diverse set of antigens (for review see Winter et al. 1994). However, phage-antibody selections on some proteins and especially on peptides are not always successful, often due to by immobilization-associated features. The main problem observed for selection on peptides is the very poor coating efficiency of some peptides and the altered availability of epitopes on plastic-coated peptides. The direct coating of proteins on plastic is usually more efficient but can also be problematic, because the passive adsorption on plastic at pH 9.6 is a mechanism of protein denaturation. Under these conditions, 95% of adsorbed proteins are non-functional (Butler et al. 1992; Davies et al. 1994). This problem is not very important for a classical ELISA because mostly a small fraction of proteins having a native conformation is still detectable. However, this phenomenon can be very troublesome for phage antibody library selections, because phage antibodies binding to epitopes only present in denatured molecules may be selected.