The transferrin receptor or transferrin-binding proteins (Tbps) of 50 strains of Neisseria meningitidis belonging to different serogroups were examined by Western blotting using two rabbit antisera raised against Tbp purified from N. meningitidis strains B16B6 and M982. On the basis of the reactivity of Tbp2 with the antisera two patterns were observed and allowed the classification of 74% of the strains in group I (M982-like strains) and 26% in group II (B16B6-like strains). Southern blot analysis was performed on the genomic DNA of 16 meningococcal strains and showed that under stringent conditions, the tbp2 probes were specific for each group identified. Both immunological and genomic analyses have led to the identification within N. meningitidis strains of two major families distinguished on the basis of the characteristics of Tbp2 molecules, independently of serogroup, type or subtype.