A method for incorporation, into the DNA that encodes a phage coat protein, of a polypeptide, where it is available for a selection procedure; especially for production and selection of antibody (even anti-self antibody) fragments directed against a specific antigen. A library of V_H or V_L genes is produced by PCR using primers directed to constant regions that flank the variable region, cloned and inserted into the gene for a phage coat protein that, when expressed, is available for cycles of growth and selection by adsorption on to an antigen-coated plate or beads.