Phencyclidine (PCP) can be detected in body fluids with very high sensitivity by gas chromatography (GC) with surface ionization detection (SID) using pethidine as internal standard. PCP was extracted with Sep-Pak C18 cartridges from whole blood and urine samples, which gave clean extracts. The calibration curve for spiked whole blood was linear in the range 1.25-20 ng/ml. The detection limit of PCP was approximately 15 pg on-column (0.75 ng/ml sample), which was much lower than by GC-nitrogen phosphorus detection. The recovery of PCP and pethidine from spiked whole blood or urine samples was above 85%. This method seems very useful for the determination of PCP in forensic and clinical toxicology.