The pharmacodynamics and pharmacokinetics of three phencyclidine analogs, differing from phencyclidine (PCP) only in the nature of the amine structure, were determined after intravenous doses of equimolar amounts to rats. The purpose of the study was to assess the role of pharmacokinetics in the in vivo potency of the compounds. The compounds examined were phenylcyclohexyl-pyrrolidine (PCPY), diethylamine (PCDE), ethylamine (PCE), and phencyclohexylamine (PCA). The behavior responses monitored included ataxia and others previously shown to be characteristic of PCP. In contrast to their relative affinities for the MK 801 binding site, the behavioral potencies of PCE, PCDE and PCPY were comparable to PCP. The major discrepancy occurred with PCDE, whose affinity for the NMDA receptor was 1/20th of PCP. The pharmacokinetic studies showed that the discrepancy between in vivo and in vitro activity of PCDE could be partially accounted for by its conversion to PCE, a relatively potent PCP-like agent.