In the Federal Republic of Germany, the morbidity curve of meningococcal infections from 1966-1984 exhibited two maxima in 1970 and 1979 representing morbidity values of 2.9 and 2.3 per 100,000 of the population, and a small peak in 1974. The average morbidity of the 19 years was 2.1/10(5), the lowest morbidity 1.3/10(5) (1983/84). Meningitis occurred on an epidemic scale in 1970 in Bremen, in 1971 in Schleswig-Holstein and 1971-1977 in the Saarland. Most cases were notified during the first four four-week periods of the year, but in two years (1967, 1969), the late-summer peak exceeded the peak of winter/spring. 17.3% of the cases occurred in infants, 51.7% in the first five years of life. Morbidity was highest during the second quarter of the first year. The sex ratio (m:f) of the infections was 1.6:1, but in the aged, morbidity was about the same in both sexes (0.9:1). The case-fatality ratio varied between 7.1% (1977) and 12.1% (1971, 1982) and averaged at 9.7%. It was highest in the aged (37.1%) and second-highest in infants (18.7%). Differences of lethality due to sex could not be demonstrated. Of 1.685 meningococcal strains isolated from CSF and/or blood, 7.3% were of serogroup A, 74.4% of group B, 15% of group C, 1.5% of group Y and 1.1% of group W135. The proportion of group B infections was highest in infants, of group A infections in children (5-10 years), of group C infections in older children and adolescents (10-20 years). The sensitivity of N. meningitidis to sulfadiazine varied with serogroup and year of isolation. Since 1977, practically all group A strains, but only 13% of group B and 9% of group C strains proved to be resistant. Practically all strains were fully sensitive to rifampicin and minocycline; results of trials with spiramycin were not in support of the use of this compound as a chemoprophylactic agent.