The distribution of plasmids in N. meningitidis strains according to t
heir origin and serological groups has been studied. Plasmids have bee
n discovered in N. meningitidis of all groups, plasmid-carrying strain
s constituting 55% of strains isolated from healthy carriers and 46.2%
of strains isolated from patients. The molecular weigth of N. meningi
tidis plasmid DNA varies from 2.9 MD to 95 MD.