BACKGROUND: We could establish a streptonigrin-resistant strain called SR-1 strain from Staphylococcus aureus ATCC 6538 as a parental strain and characterize SR-1 strain as defective in the iron-uptake mechanisms including production of siderophores and expression of transferrin-binding protein on the cell wall. We performed this study to elucidate effect of the iron-uptake mechanisms on the growth in human body fluids. METHODS: Growth kinetics of SR-1 strain were compared with those of the parental strain and the increase of unsaturated iron-binding capacity (UIBC) was measured. Siderophore production and expression of transferrin-binding protein were detected by CAS diffusion assay and ligand-blot method probed with human transferrin conjugated horseradish peroxidase, respectively, as the strains were cultivated in normal pooled sera, ascitic fluid and pleural effusion. RESULTS: Siderophores activity in the body fluids could not be detected by the CAS diffusion assay. The parental strain expressed the transferrin-binding protein on the cell wall during the growth in ascites and pleural effusion except the sera whereas SR-1 strain did not. Growth kinetics showed that SR-1 strain grew sluggish compared to the parental strain. The peak of increase of UIBC of the parental strain was observed at the mid-exponential growth phase and the increase of UIBC of SR-1 strain was either lower than that of the parental strain or not changed. CONCLUSION: The iron-uptake mechanisms of S. aureus, especially expression of transferrin-binding protein, play a significant role in growing in the body fluids.