The effect of fornix lesions on some effects of manipulating the context on performance in extinction were studied. In renewal, subjects' responding to an extinguished conditioned stimulus (CS) recovered when the CS was presented in the context in which it had been conditioned after extinction in a different context. In reinstatement, it recovered when the CS was tested after independent presentation of the unconditioned stimulus (US; an effect mediated by contextual conditioning.) In spontaneous recovery, it recovered after the passage of time, that is, when the CS was tested in a new temporal context. In the conditioned suppression method, fornix lesions had no effect on conditioning, extinction, renewal, or spontaneous recovery; however, they abolished the reinstatement effect. The results suggest that the hippocampal system may be important in the formation of context-US associations, but not in other types of learning about the context.