Three experiments investigating second-order conditioning were conducted with rat subjects. An appetitive Pavlovian conditioning situation was employed in which the response measure was the amount of general activity. Experiment 1 provided a well-controlled demonstration of substantial second-order conditioning. In Experiment 2 extinction of the first-order conditioned stimulus (CS) has no effect upon the response to the second-order CS. Experiment 3 examined the relationship of the second-order conditioning paradigm to that of conditioned inhibition. Both phenomena could be observed simultaneously in the same setting. Implications for second-order conditioning and related conditioning phenomena are discussed.