Multi-resistant serotype 23F pneumococcal strains from an outbreak in a day-care centre in South Africa and strains from sporadic cases in Korea were analysed for their relatedness, by means of arbitrarily-primed PCR (AP-PCR), repetitive extragenic palindromic PCR (rep-PCR) and penicillin-binding protein (PBP) gene profiles. The South African strains previously shown to be identical to the 23F Spanish clone had identical AP-PCR and rep-PCR patterns to 13 Korean isolates. PBP gene analysis of strains from this cluster showed identical fingerprints, suggesting clonality. Isolates, identical genotypically to the 23F clone appeared to have acquired the type 19F and 14 capsular serotypes, respectively, a result that suggests horizontal transfer of capsular biosynthetic genes. These same techniques revealed three serotype 9V isolates not closely related to the 23F clone but which harbour PBP genes identical to the 23F clone. The data presented suggests that a clone of S. pneumoniae serotype 23F related to isolates from Spain and South Africa has become disseminated in Korea.