Somatic, endocrine, and behavioral correlates of growth and levels of voluntary running activity were measured in adult hamsters with hippocampal transections (HIPPO cuts) or in controls with transections of overlying cortex. Significant increase in serum concentration of growth hormone (GH) and decrease in pituitary concentration of GH were measured in HIPPO hamsters with a homologous radioimmunoassay method for hamster GH. HIPPO hamsters had increased: serum insulin concentration in fed state, food consumption, ponderal and linear growth, and percentage of body fat, and decreased levels of voluntary activity. Similarities between growth acceleration after HIPPO cuts and lesions of rostral medial septum suggest that fibers interconnecting, or passing through, the hippocampal formation and septum inhibit growth in adult hamsters.