Staphylococcus aureus is one of the most important pathogens both in community- or hospital-acquired infections. The first part of this study analyzed the similarity of molecular types of S. aureus isolates cultured from nares and blood in patients with S. aureus bacteremia (SAB) by pulse-fielded gel electrophoresis (PFGE) of digested chromosomal DNA by Sma I at Kaohsiung Veterans General Hospital from August 1, 2000 through July 31, 2001. The results showed that the PFGE types of 78 (82.1%) paired nare and blood isolates of the 95 SAB patients having nasal carriage of S. aureus were clonally identical; identical in 89.7% patients of nosocomial group and 62.9% in community-acquired group. This provides the powerful evidence in close relationship between nasal carriage of S. aureus and acquisition of it in bacteremia. The data also showed that the rate of methicillin resistance occurred in SAB patients with nasal carriage in isolates of nosocomial SAB was 85.3%, and 31.3% in community-acquired group. The second part of this study analyzed the distribution of PFGE types of 163 nosocomial SAB isolates. The most predominant type was type A and composed 51.5% (84 strains) of 163 nosocomial SAB isolates. They were further divided into 7 subtypes. The second prevailing type was type B, 6.1%(10 strains). The evidence that an endemic stain (type A) occurred in >50% of nosocomial bacteremic isolates demonstrates horizontal dissemination of a single endemic strain of S. aureus in the SAB patients was common in the hospital. These results provide support for strategies to endorse more intensive procedures in infection control and to prevent systemic S. aureus infections by eliminating S. aureus nasal carriage.