Alpha-1 acid glycoprotein or orosomucoid is a plasma protein whose characteristics are associated with a high abundance of bound N-glycans of different complexity that are arranged across five different glycosylation sites on the protein and contribute to roughly 45% of its total mass. Although the biological role of AGP is not completely elucidated, the effect of the composition of the bound N-glycans and the changes in its glycosylation are related with different immunomodulatory, anti-inflammatory and pathological processes. In addition, its ability to bind drugs makes it, alongside albumin, the most important serum transport protein and it has a major effect on the bioavailability of those drugs. One of the drugs for which it is assumed that the N-glycome of AGP affects its binding affinity is warfarin. Warfarin is a relatively old drug, but even today it is the most proscribed drug in anticoagulant therapy, despite its complicated dosing regime and numerous interactions with other drugs. It is a highly potent drug and considering its narrow therapeutic range and expressed inter-individual differences in therapy, it is required to continuously do laboratory tests which ensure optimal dosing, as well as reduce the risk of a blood cloth or bleeding when the dose is too low or too high, respectively. One of the reasons for dose variability in warfarin therapy, besides many non-genetic factors, was found in genetic polymorphisms of the enzymes CYP2C9 and VKORC1. By taking into consideration unique clinical and genetic information, one of the fundamental determinants of personalized medicine, and by striving towards therapy individualization, pharmacogenomic tests are proposed to be conducted for the aforementioned enzymes with the aim to optimize warfarin therapy. An in vitro study on asialo-AGP demonstrated that high branching and fucosylation of its N-glycans reduces the binding affinity of warfarin. This study wanted to analyze the effect of human AGP N-glycosylation on the dosing of warfarin during therapy in vivo. The method which was used for the enrichment of AGP from plasma samples of patients who take different doses of warfarin included precipitation using acids and proteolytic cleavage using trypsin. The AGP glycopeptides were further enriched with solid phase extraction and analyzed using a reverse-phased LC-MS method. The results of the regression analysis, which was used to demonstrate the connection between AGP N-glycosylation and warfarin dosing, have showed a statistically significant change only at the glycosylation site IORMIF for bi-antennary N-glycans, but, although not statistically significant, a trend was visible in which higher branching and fucosylation of AGPs N-glycans result in the need for a lower warfarin dose. The conducted in vivo research has partially confirmed the results of the in vitro study. However, in order to prove the clinical significance of N-glycosilation change in AGP with warfarin dosing further research with a greater and more representative sample size as well as more sophisticated statistical methods is needed.