Monoclonal antibodies prepared against clathrin-coated vesicles cargo molecules were screened for their ability to precipitate the mAChR binding activity present in a light-density smooth membrane fraction from bovine brain called peak I. Only monoclonal antibody 10C7 was able to selectively sediment 38% (+/- 4.2) of the mAChR binding activity of peak I. Analysis by competition experiments of the supernatant obtained after the immunoprecipitation step reveals that neither the ratio of high/low affinity sites, nor the affinity ratio KH/KL was significantly altered for either of the muscarinic antagonists. The data implies that the bovine brain smooth-membrane compartment(s) expressing the mAb 10C7 antigen is also enriched in M1 and M2 mAChR.