The hippocampal electrical activity and behavior of rabbits have been studied in the presence of novel and emotional stimuli. The effects of these stimuli have been recorded in controls and in groups of animals treated with ACTH (4–10) (10 µg/100 g, i.m.) and ACTH (1–24) (10 µg/100 g, i.m.). Recordings were made immediately and 30 min after injection. ACTH (4–10) injection failed to evoke any significant behavioral or electrical response. Rabbits recorded 30 min after ACTH (1–24) injection showed a reduction of hippocampal RSA (rhythmic slow activity) frequency and behavioral activity. In particular, reduction of exploration, self-grooming, motor activity and approaches to the new object have been observed. Since ACTH is characterized by a corticotropic action these results can be due to corticosteroid st