Phencyclidine was determined by gas chromatography selected ion monitoring in six dogs and seven monkeys. Aliquots of venous blood were taken over 4 h in the monkey after 1.1 mg kg-1 and over 24 h in the dog after 1.0 mg kg-1 of phencyclidine i.v. Pentadeuterated phencyclidine was used as the internal standard. In the electron impact mode the most abundant fragments in the mass spectrum of phencyclidine were m/e 91 and 200, and 96 and 205 in the [2H5]phencyclidine spectrum. These fragments were used to quantitate the amount of phencyclidine present. In both species, a complex exponential decline of plasma phencyclidine was found in most animals that fit a two compartment open model. In monkeys, the mean half-life (beta phase) was 2.36 h and in the dog it was 2.86 h. Compared with the monkey, the dog considerable emergence delirium. The two species had rather different pharmacokinetics which may be relevant to the observed differences in degree of anesthesia and recovery.