A sensitive and specific assay for the quantitation of phencyclidine (PCP), its several metabolites, and derivatives in biological samples is described. The method is based on the extraction of PCP and related compounds with organic solvents followed by gas chromatographic (GC) separation with nitrogen-phosphorous (NP) detection of the extract derivatized with heptafluorobutyric anhydride. The detection limit was about 5 pmol per injection with a linear standard curve to 16 nmol in the initial sample. The recovery of different compounds ranged from 80 to 98%. Precision of the method was within 3 to 5%, while day-to-day variations did not exceed 5%. The present procedure permits the identification and quantitation of PCP and its major primary and secondary metabolites. In addition, several PCP analogs and derivatives that are not recognized as PCP metabolites can be quantitated using this procedure. The assay was applied for the quantitation of PCP and its metabolites in tissue homogenates and body fluids of PCP-dosed animals as well as in the urine of PCP-intoxicated humans. An in vitro system for PCP biotransformation studies by liver and placental microsomes was also developed.