Objective:The role of norepinephrine (NE) on growth, adhesion and invasion of methicillin-resistant Staphylococcus aureus (MRSA) ATTC 43300 was examined in human osteoblast (HOB) cells. The effects of NE and/or MRSA on the viability and cell death pathways of HOB cells were also investigated. Furthermore, the alterations of bacterial response to oxidative stress (H 2 O 2 ) were analyzed in the presence/ absence of NE.Materials and Methods: Bacterial growth was detected spectrophotometrically. The colony counting method was examined for adhesioninvasion. The alteration of HOB cell viability was determined by methyl thiazolyl diphenyl-tetrazolium bromide (MTT) assay. The death pathways of HOB cells were examined microscopically using acridine orange-ethidium bromide dual staining and dichlorofluoresceindiacetate (DCF-DA) dye. The bacterial response to H 2 O 2 was investigated by agar dilution. Results:The growth of bacterium was not affected in the presence of NE. Bacterial adhesion was decreased by NE (p<0.0001) while highlevel NE induced invasion (p=0.013). HOB cell viability was reduced by MRSA and/or NE (p<0.001). MRSA and co-existence of MRSA and NE caused necrosis more than apoptosis in HOB cells (p<0.05). NE did not alter the bacterial response to oxidative stress. Conclusion:Norepinephrine has different effects on the biological properties of both MRSA and HOB cells.