A chronic hepatitis B virus (HBV) infection causes life-threatening complications including cirrhosis, cancer and severe hepatitis. These complications are all associated with mutations in viral proteins. Identifying these mutations contributes to both our understanding of how the HBV causes complications and to current management strategies for patients in the clinic. The current method for detecting mutations in proteins is dependent on predicting their presence from analyses of viral DNA sequences. There are two problems with this. The first is that viral DNA is not always available for analysis. The second is that mutations predicted to be found by analysing DNA sequences are not always found in viral proteins. Thus this method can be inaccurate. The purpose of this research is to use a technology called mass spectrometry to directly identify mutations in samples of viral protein; which are always available and will produce more accurate results with immediate clinical impact.