The aims of this study were to assess the nasopharyngeal colonisation rate, serogroup and antibiotic susceptibility patterns of Strepto-coccus pneumoniae strains isolated from healthy children. Of 848 children, 162 (19.1 %) were found to be carriers. The carrier rate was significantly higher in the 7-year-old age group. Children from the slums of the city had higher carriage rate (23.7%) than those in the centre of the city (17.7%), but this was not statistically significant. The number of intermediate penicillin-resistant strains was 17 (10.5%). No high-level penicillin-resistant S. pneumoniae strain was found. The rates of resistance to co-trimoxazole, erythromycin, tetracycline and clindamycin were 11.7%, 4.9%, 4.3% and 3.7%, respectively. All isolates were uniformly susceptible to rifampicin, moxifloxacin, levofloxacin and vancomycin. Fourteen different serogroups were identified. The most prevalent serogroups in descending order were 9, 19, 23, 10, 6 and 18, accounting for 76.3% of the isolates. Arbitrarily primed polymerase chain reaction typing of 105 isolates revealed that 25 (23.8%) of the isolates were clonally indistinguishable. This value was 20.9% in children from the central area and 36.8% in those from the slum of the city. There was no relationship between serogroups and genotypes, i.e. strains within the same serogroup yielded the same or different genotypes, and vice versa. In conclusion, serogrouping results give a preliminary idea about the possible coverage of a future pneumococcal vaccine. Penicillin G is still a suitable agent for the empirical treatment of pneumococcal infections in our population. Living in the slum of the city may lead to both increased carriage and clustering rates of S. pneumoniae among healthy children. (c) 2005 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.