A simple and rapid (extractionless) high-performance liquid chromatographic method with UV detection, at 330 nm, was developed for the simultaneous determination of piroxicam and its major metabolite, 5'-hydroxypiroxicam, in human plasma and urine. Acidified plasma and alkali-treated urine samples are used and naproxen is added as internal standard. The separation is performed at 40 degrees C on a C18 Spherisorb column with acetonitrile--0.1 M sodium acetate (33:67, v/v, pH 3.3) as mobile phase. The retention time is 2.2 min for 5'-hydroxypiroxicam, 2.6 min for piroxicam and 3.2 min for naproxen. The detection limit is 0.05 micrograms/ml using a 100-microliters loop.