In 3 experiments, the role of adrenal corticosterone in schedule-induced wheel running was investigated. Data from the first experiment showed that bilateral adrenalectomy significantly suppressed schedule-induced wheel running, but did not influence non-scheduled wheel running. Results from a second experiment, where bilateral adrenalectomy with and without replacement of corticosterone was used, showed that the suppressant effect of adrenalectomy on schedule-induced wheel running was completely reversed by replacement of corticosterone. In experiment 3, plasma corticosterone levels of all experimental rats were determined at the completion of the last test session. The results showed that a circulating level of corticosterone was necessary for the occurrence of schedule-induced wheel running. These findings show that adrenal corticosterone is involved in the regulation of schedule-induced wheel running.