Authors study 464 strains of N. meningitidis isolated from cerebrospinal fluid and/or blood of children with meningococcal disease in a childrens' hospital in Barcelona from January 1979 to September 1986. These strains are distributed in four serogroups and eight serotypes, being serogroup B and serotype 2 the most frequent ones. Authors have isolated 4 strains with decreased penicillin susceptibility, three with a MIC of 0.2 microgram/ml and one with a MIC of 0.4 microgram/ml. All four belong to serogroup B, three to serotype 1 and one was non-typable. This alert on possible therapeutic failures that could emerge in next future and implies the necessity of in vitro testing susceptibility of all strains of N. meningitidis isolated from pathologic products in order to detect possible resistances.