All samples were analysed using high performance liquid chromatography (HPLC) to determine the concentrations of paracetamol and its metabolites, paracetamol glucuronide, paracetamol cysteine, paracetamol sulphate and paracetamol mercapturate. Urine samples were prepared for HPLC by centrifuging at 2000rpm and then diluting the supernatent 1 in 10 with mobile phase. This was injected directly onto an Aqua C18 reversed phase column, 250mm x 4.6mm i.d. with a 5 micron pore size (Phenomenex) via a C18, 5 micron guard column. The mobile phase used was 7% acetonitrile – 93% orthophosphoric acid (20mM pH 6.7) at a flow rate of 1ml/min using a Shimadzu LC10-AT pump and a Shimadzu SPD-10AV ultraviolet absorbance detector operating at 254nm. Calibration curves were constructed for each of the metabolites and paracetamol in blank urine using the peak area and were linear over the range 0.05 – 5mM. The method was found to be reproducible with a coefficient of variation of 2.6%. The metabolites of paracetamol; glucuronide, cysteine, sulphate, mercapturate and paracetamol itself eluted in 3.9, 8, 10.2, 12.2 and 13.4 minutes respectively. Reference samples of paracetamol cysteine, sulphate and mercapturate were kindly supplied by Dr Anthony R. Temple MD, McNeil Consumer Healthcare, Camp Hill Road, Fort Washington, Pennsylvania, USA.