[14C]2-deoxyglucose autoradiography was used to show cerebral and regional cerebral metabolism during slow-wave sleep (SWS) and rapid-eye-movement sleep (REM) in the cat. Lower levels of mean cerebral metabolism, reflecting cerebral energy conservation, were associated with SWS. A clear link between REM and mean cerebral metabolism was not observed. At the regional level, SWS was associated with markedly low metabolism in thalamic sensory relays and in cortex. REM was associated with relatively low metabolism in the cerebellum, but with relatively high metabolism in the hippocampus, and in some 'motor' regions including the trigeminal and red nuclei. Thus, SWS was linked to cerebral energy conservation and to particularly low levels of functional activity in cortical and sub-cortical sensory regions. REM was unlike SWS in that: REM did not appear to be strongly linked to cerebral energy conservation; REM was linked to metabolism in fewer brain regions than was SWS; and most REM-linked regions exhibited relatively high levels of metabolism. In addition, while SWS was most clearly associated with functional activity in sensory regions, REM was linked to functional activity in a small number of limbic and motor regions. In sum, SWS and REM are associated with distinctive cerebral metabolic and functional states.