Summary The exotoxin pertussis toxin (PT) produced by virulent Bordetella pertussis bacteria is regarded as the main virulence factor of the organism and held responsible for most of its pathological effects. Identification of functional sites on PT would greatly facilitate site‐specific detoxification and thus also the development of a new vaccine. For the investigation of structure‐function aspects of PT we have prepared and characterized eleven monoclonal antibodies (mAbs) (UB‐A1, UB‐A2, UB‐A10, UB‐B7, UB‐B12, UB‐D4, UB‐D7, UB‐D10, UB‐F7, UB‐G1, and UB‐G12) directed at the native toxin. Only UB‐B12 and UB‐D10 recognized PT in Western blotting indicating that most of the mAbs were directed against conformational epitopes. The mAbs were assayed for their ability to interfere with the binding of PT in model receptor systems like a solid phase binding assay using fetuin as receptor moiety, hemagglutination of chymotrypsin‐sensitized goose erythrocytes, and the PT‐mediated induction of the clustered growth pattern (CGP) of Chinese hamster ovary (CHO) cells. Five of the eleven mAbs (UB‐A1, UB‐A2, UB‐B7, UB‐B12, and UB‐D7) interfered with the binding of PT to fetuin on solid phase and with PT‐mediated hemagglutination. UB‐A2, UB‐B7, and UB‐B12 also inhibited the induction of the clustered growth pattern of CHO‐cells. This indicates that the determinants recognized by these mAbs are associated with the formation of the carbohydrate recognition sites of PT. Thus, the monoclonal antibodies described in this study will be valuable tools in the further analysis of the structure‐function relationship of pertussis toxin with respect to receptor recognition and binding.