The aim of the present study was to determine the effect of major surgery on paracetamol glucuronidation and sulfation. 53 patients were given doses of either 1, 1.5 or 2 g of paracetamol by intravenous (IV) infusion. A combination of rich and sparse plasma and urine samples were collected over a 7 day period (Day 0 being preoperative collection and Days 1 to 6 being postoperative collection) for up to 12 hours after each dosing. The samples were analysed by high-pressure liquid chromatography to determine the amount of paracetamol and metabolites. The data were modelled in Phoenix NLME using a user-defined population parent-metabolite model with linear disposition. The results of this study will be presented at the PAGANZ 2012 Scientific Meeting.