The uptake of radiolabelled 2-deoxyglucose (2DG) was used to compare the effects ofthe steroid anaesthetic, Althesin (alphaxalone plus alphadolone acetate) with those of sodium pentobarbitone on the regional metabolism of the brain and pituitary gland. Experiments were carried out on adult female Wistar rats. Studies on conscious animals were carried out with the aid of an indwelling intra-atrial catheter. The uptake of 2DG was measured both by liquid scintillation spectroscopy of <sup>3</sup>H-2DG in tissue blocks and by quantitative autoradiography with <sup>14</sup>C-2DG Both anaesthetics significantly reduced uptake of <sup>3</sup>H-2DG in the frontal, parietal and occipital cortex, and striatum and thalamus, but <sup>3</sup>H-2DG uptake was significantly increased in the pituitary gland. Similar effects were found by measuring <sup>14</sup>C-2DG uptake, and this technique showed further that Althesin, but not sodium pentobarbitone, selectively increased (2-fold) the uptake of <sup>14</sup>C-2DG by the pars intermedia. The increase in <sup>I4</sup>C-2DG uptake by the pars intermedia in animals anaesthetized with Althesin was significantly reduced by a lesion placed in the arcuate nucleus. The most likely explanation for the effects of Althesin on the pars intermedia is that this anaesthetic increases the activity of arcuate neurons that innervate the pars intermedia.