Plasma GH responses, as measured by radioimmunoassay, were assessed in individual rats with indwelling jugular cannulae following administration of pentobarbital sodium (Pb) (50 mg/kg i.p.) Plasma GH levels rose within 5–10 min after Pb and returned to baseline levels in most animals by 20–30 min. GH release was blocked by either VM hypothalamic lesions or by medial basal hypothalamic deafferentation. Depth EEG recordings from the hippocampus, basolateral amygdala and in some cases from the VM, showed high voltage, spike and sharp wave activity maximal at a time coincident with GH release. These results indicate that Pb-induced GH release is mediated by neural mechanisms, and suggest further that extra-hypothalamic structures may be involved in activation of the response.