Seven years after meningococci were first grown from patients with meningitis (1 ), Kiefer reported the isolation of the organisms from the nasopharynx of cases of meningococcal disease, and from their contacts (2 ). The importance of nasopharyngeal acquisition and carriage as a key step in the development of invasive meningococcal infection was rapidly appreciated, as was the far greater frequency of the carrier state when compared with the relatively small numbers of individuals developing invasive disease. Attempts to interpret the significance of variations in the bacteria themselves as a factor influencing the outcome of the interaction between humans and meningococcus had to await the development of the first typing systems based on serological reagents (3 ). It became clear rapidly that meningococcal strains isolated from the blood or cerebrospinal fluid (CSF) of patients with invasive disease were more likely to be typable than strains from the nasopharynx of individuals who were asymptomatic carriers.