We report on the immunochemical characterization of two antibodies engineered to express RGD, a peptide from adhesive proteins of the extracellular matrix. One or three RGD motifs were introduced in the third complementarity-determining region (CDR) of a murine heavy (H) chain variable (V) region gene yielding two antibodies, gamma 1RGD and gamma 1(RGD)3. A murine monoclonal antibody (mAb) raised against an RGD-containing synthetic peptide bound in Western blot the H chain of both gamma 1RGD and gamma 1(RGD)3. Pronectin F, a genetically-engineered polymer containing RGD, abrogated this binding. Anti-idiotypic antibodies against the (RGD)3 loop were generated in a rabbit by immunization with gamma 1(RGD)3. Anti-idiotype antibodies purified by affinity-chromatography on the synthetic peptide GRGDSPC reacted in ELISA with gamma 1(RGD)3 and human fibronectin. Adhesive proteins, unlike RGD-containing synthetic peptides, were able to interfere with the interaction between gamma 1(RGD)3 and the anti-idiotypic antibodies. These results suggest that it is possible to genetically engineer the hypervariable loops of immunoglobulins and confer them new idiotypic characteristics. These results support the concept of antibody mimicry.