A prospective study was undertaken with the purpose of finding out the proportion of pharyngeal carriers of N. meningitidis and N. lactamica among our infantile school population. Seven groups constituted by, approximately, 200 infants each, were studied along two years. Samples were taken in two different schools, for each each group, at a period of average incidence (February, April, June and October). Infants were between five and six years of age and made a total of 1,315 individuals, which we consider representative of our school infantile population. Positivity for N. lactamica was around 20%, whereas 10% of infants were carriers of N. meningitidis. Among the latter 56% were group B, 15% group Y, 5% group A and 20% agglutinated spontaneously. The remainder fell into several serogroups (10 unclassifiable, six 29E and one each, X, W135 and Z). Concerning group B serotypes, except for 22 not typable cases, most carriers were serotype 2, while the remainder were distributed in seven other serotypes. These findings are comparable to those seen in the population with clinical disease. However the number of carriers remained constant and, in contrast to what happened with clinical patients, was unrelated to seasonal variations. Resistance of N. meningitidis to chemotherapy was the following: sulfadiazine 100%, ampicillin 19%, rifampicin 20% and penicillin 0%. The latter can not be considered a good choice in prophylaxis.