Extensive clinical experience with ehlorpromazine and its congeners testifies to the ability of such agents to reduce agitation and manifestations of anxiety in human subjects. Although greatest emphasis has been placed on its effect on psychotic behavior, WIKLER finds that "in the treatment of psychoneuroses, there appears to be general agreement that chlorpromazine is useful as a palliative and as an aid to psychotherapy." Relief of symptoms and enhancement of psychotherapy during chlorpromazine treatment of neuroses are both generally attributed to some inhibitory effect of the drug on emotional excitability.
Animal experimentation has yielded evidence for seemingly analogous effects of chlorpromazine on the emotional state of infrahuman subjects. The most common demonstration of an inhibition by chlorpromazine of fear-or anxiety-associated behavior has been the conditioned avoidance response (CAR). Inhibition of the acquisition of an avoidance response in rats was shown by Lu et al. Selective inhibition of performance of the fear-motivated CAR over the pain-motivated escape response has been demonstrated repeatedly in rats by Cook and WEIDLEY, COURVOISlER, McMu~AY and JAQUES, 1%. E. MILLE~ et al., (1957), and others. The CAR test has been widely used for the characterization of potential new "psychoactive agents" in spite of differences among psychologists in their interpretation of the events involved in avoidance conditioning and in spite of uncertainty of the mechanism of drug effects on the CAR.
Interpretation of the basis for learning and performance of the CAR, as stated by MclVfvRRAY and J~Qu~s, and others, is usually based on the stimulus-response concept of learned behavior and on the drivereduction hypothesis of reinforcement as propounded by N. E. MILLER. This interpretation is presented diagrammatically in Fig. 1 a and may be summarized with pharmacological emphasis as follows: (1) an escape response to a shock stimulus is learned; (2) concurrently, unconditioned fear responses evoked by shock become conditioned to an exteroceptive * This study was aided by a grant from the University of Oklahoma Research Committee.