This chapter will describe the use of the immunoblotting method for analysing antibody specificities towards meningococcal antigens in sera from vaccinees, receiving group B meningococcal outer-membrane vesicle (OMV) vaccines, or from patients, falling ill with meningococcal disease. The power of the blotting technique lies in the simultaneous identification of many immunogenic components in a sample. Within the meningococcal field, this method has been employed in analyzes of antibody specificities of sera from vaccinees (1 –6 ), patients (7 –10 ), and carriers (11 ,12 ) as well as for characterization of OMV vaccines (13 ,14 ). Some of these studies present various ways of quantifying the blotting results (5 ,7 ,9 ,11 ).