A molecular recognition code has been hypothesized to exist in which ligands and their binding sites are encoded on complementary segments of genomic DNA. We have tested this hypothesis by generating a rabbit antibody to a synthetic decapeptide (complementary peptide) encoded by an RNA complementary to the mRNA for luteinizing hormone-releasing hormone (LHRH) and determining whether this antibody recognizes the LHRH receptor. When the antibody was used for immunoperoxidase staining of enzymatically dispersed rat anterior pituitary cells, only those that contained and secreted luteinizing hormone (i.e., the gonadotropes) were recognized. This staining could be abolished by preincubation with the complementary peptide or with an LHRH agonist, suggesting that the antibody is specific to the complementary peptide and is directed at the binding site of the receptor. Further evidence that the antibody recognizes the LHRH receptor was obtained in immunoblot experiments on solubilized receptor from pituitary glands. Immunoperoxidase staining with the antibody revealed two bands at 60 kDa and 51 kDa, which are values similar to those previously obtained for the LHRH receptor in photoaffinity-labeling experiments. The staining of these bands was inhibited by preincubation with the complementary peptide or an LHRH agonist. The antibody as well as the complementary peptide to LHRH also suppressed LHRH-stimulated luteinizing hormone release in a quantitative reverse hemolytic plaque assay, presumably by binding to the LHRH receptor and by binding LHRH, respectively. These findings suggest that the synthetic decapeptide whose sequence is specified by the complementary RNA to LHRH mRNA is sufficiently similar to an LHRH binding site that the peptide not only binds LHRH but was also recognized by the immune system as such a site. These findings provide strong support for the hypothesis that recognition molecules are encoded by complementary segments of genomic DNA.