We recently managed an infant with meningitis caused by Streptococcus pneumoniae in whom ceftriaxone failed to sterilize the cerebrospinal fluid after 6 days of therapy. This strain, which had a penicillin minimal inhibitory concentration (MIC) of 2 micrograms/ml, appeared susceptible to ceftriaxone (MIC < 0.5 micrograms/ml) when evaluated by a commercial MIC panel (Microtech Medical Systems, Inc., Aurora, CO) but was found to have a ceftriaxone MIC of 4 micrograms/ml when evaluated by conventional microtiter broth dilution technique. Furthermore ceftriaxone therapy of meningitis induced with this strain in a rabbit model was ineffective. Thirteen of 112 pneumococcal strains (11.6%) isolated recently at Children's Medical Center of Dallas were penicillin-resistant, and 3 of these were highly penicillin-resistant (MIC > or = 2 micrograms/ml). The incidence of pneumococcal strains with cefotaxime MICs > or = 1.0 micrograms/ml has increased from 0 of 258 from 1981 to 1983 to 5 of 112 (4.5%) from 1991 to 1992. The definition of cephalosporin resistance for pneumococci requires modification and further studies of the antibiotic management of meningitis caused by such strains are needed because resistance to cephalosporins is increasing and the extended spectrum cephalosporins may be ineffective as sole therapy.