A sensitive, specific and rapid determination of 5-(4-chlorobenzoyl)-1,4-dimethyl-1H-pyrrole-2-acetic acid sodium salt dihydrate (zomepirac sodium, Zomax) in human plasma and urine by a continuous body fluid monitoring system based on high-performance liquid chromatography is described. Samples are directly injected into the apparatus which consists of commonly available HPLC-modules. Manual sample clean-up procedures as well as the addition of an internal standard are not needed. Using 50-microliter aliquots, the detection limit is lower than 0.05 microgram/ml and the calibration ranges from 0.5 to 100 micrograms/ml are linear for both, spiked samples and references. The recovery is 97% for plasma and 95% for urine samples at a sampling rate of about 15 samples/h.