Gas chromatography (GC)/surface ionization organic mass spectrometry (SIOMS) has been found to give much higher sensitivity for measurements of phencyclidine (PCP) than the conventional GC/electron impact (EI)-mass spectrometry (MS). Thus, we have established a detailed procedure for measurements of PCP in body fluids by both mass chromatography and selected-ion monitoring (SIM) of SIOMS using pethidine as an internal standard (IS). Good linearity was found in the range of 0.25-10 ng/mL of whole blood or urine, when measured by mass chromatography, and in the range of 0.025-1.0 ng/mL of whole blood by SIM. The recoveries of PCP and IS spiked to whole blood were 106 +/- 17% at 1 ng/mL and 113 +/- 11% at 5 ng/mL; that of IS was 97.8 +/- 10.4% at 5 ng/mL. The detection limits (signal-to-noise ratio = 3) were estimated to be 0.05 ng/mL of whole blood or urine by mass chromatography and 0.01 ng/mL of whole blood by SIM. The coefficients of intraday and interday variations were not greater than 10.3%. We could detect PCP from rat whole blood 2 h after subcutaneous injection of PCP (1 mg/kg) by mass chromatography. The mean PCP concentration in rat blood was 47.7 +/- 6.2 ng/mL (mean +/- SD, n = 4).