Updated project metadata. Giardia duodenalis is a protozoan parasite of the small intestine in vertebrates, including humans. Assemblage A of G. duodenalis is one of two discrete subtypes that infects humans, and is considered a zoonotic assemblage. Two G. duodenalis Assemblage A strains BRIS/95/HEPU/2041 and BRIS/83/HEPU/106, constituting virulent and control strains respectively, were analysed in one of the first comparative shotgun proteomic studies performed in this parasite. Protein extracts were prepared using a multiplatform approach with both an in-gel and in-solution sample preparation to enable us to assess the complementarity for future Giardia proteomic studies. Protein analysis revealed that BRIS/95/HEPU/2041 possessed a wider and more varied repertoire of variant surface proteins (VSPs), which are hypothesised to be involved in host adaptation, immune evasion and virulence. A total of 38 VSPs were identified, with 3 common to strains, 6 unique to BRIS/83/HEPU/106 and 26 unique to BRIS/95/HEPU/2041. Additionally up to 25.6% of all differentially expressed proteins in BRIS/95/HEPU/2041 belonged to the VSP family, a trend not seen in the control BRIS/83/HEPU/106. Greater antigen variation in BRIS/95/HEPU/2041 may explain aspects of virulence phenotypes in G. duodenalis, with a highly diverse population capable of evading host immune responses.