Six hybridomas secreting monoclonal antibodies that are specific for the N-terminal peptide sequence of the murine Ah receptor were isolated. These antibodies bind with high specificity to the Ah receptor on protein blots of Hepa 1c1c7 cytosol. Three IgG1 antibodies (Rpt 1, 2, and 3) were capable of detecting 2 ng of receptor using peroxidase-goat anti-mouse IgG antibody conjugate on a protein blot. Monoclonal antibody Rpt 9 exhibited the greatest ability to immunoprecipitate the nondenatured 9S form of the Ah receptor and to visualize the AhR on liver tissue sections using immunohistochemical techniques. All of the monoclonal antibodies produced were able to bind to the mouse, rat, and human Ah receptor. These monoclonal antibodies should be useful in a wide number of applications in the study of Ah receptor biochemistry.