Ceftriaxone showed high in-vitro activity against 119 penicillin-sensitive, penicillin-resistant and rifampicin-resistant UK isolates of meningococci. Unlike ciprofloxacin and minocycline, ceftriaxone is suitable for use in young children or in pregnancy and should be considered for therapy or prophylaxis in an outbreak of meningococcal disease. The E test gave results comparable to those given by broth microdilution method in the determination of meningococcal susceptibility to antimicrobials. It is convenient for use in small laboratories and can be used to determine antimicrobial subgroups of meningococci.