During the first 6 months of 1978, 114 strains of Neisseria meningitidis isolated from patients in Norway were serotyped. Among 27 group C strains, type 2 was most common, whereas 82% of the 82 group B isolates did not react with antisera to the standard serotypes 1 to 12. These strains were shown to belong to a new serotype, type 15. Also some group A and C strains had the type 15 antigen. Investigations on a possible immunoprophylaxis against group B meningococcal disease in Norway should accordingly proceed with type 15 rather than with type 2 meningococci.