Gray and Appignanesi reported that conditioning to an element of a compound conditioned stimulus (CS) was facilitated when the compound not only preceded the unconditioned stimulus (US) but was briefly reinstated shortly after US termination. The manipulation was embedded in a "blocking" design, and the effect was interpreted as being peculiar to such a situation. The present study reports five experiments, using rats in a conditioned emotional response (CER) paradigm, aimed at further evaluating the effects of CS reinstatement. In a blocking experiment patterned after that of Gray and Appignanesi, reinstatement was observed to have a decremental rather than an incremental effect on conditioned responding. In four experiments involving simple conditioning with unitary CSs, reinstatement was observed to have either an incremental or decremental effect, depending upon the subject's preconditioning responsiveness to the CSs involved. Possible mechanisms for such variable effects are discussed without obvious resolution.