SummarySerum samples were collected from 113 healthy Caucasian volunteers before and after vaccination with meningococcal polysaccharides (MPS) group A and group C. Antibodies to MPS group A and group C were measured and sera were typed for several Gm and Km (1) allotypes. A significant association was found between the Gm 1,3,17; 5,13,14,21 phenotype and low immune responsiveness to MPS group A. These results suggest the possible existence of an immunoglobulin allotype‐linked immune suppression (Is) gene(s) in ma