A rapid and sensitive high-performance liquid chromatographic procedure is described for the simultaneous determination of piroxicam and its main metabolite,such as 5-hydroxypiroxicam, in plasma and urine. Acidified plasma (pH 3.0) was extracted with ethyl ether and indomethacin was used as an internal standard. The organic extract was reduced to dryness, the resultant residue redissolved in the mobile phase, and aliquots of this solution chromatographed on a Lichrosorb RP-18(7 μm) column using a mobile phase consisting of an acetonitrile-water-acetic acid(58 : 38 : 4) mixture. The flow rate was 1.2 ml/min and the effluent was monitored at 365 nm with 0.02 aufs. The sensitivities of this method were 0.05μg/ml levels of Piroxicam and 5-hydroxypiroxicam in the plasma and urine samples.