Materials and Methods.-Male Wistar rats, 180-220 gm in weight, were anes-thetized with sodium pentobarbital (50 mg per kg body wt) 18-24 hr after food deprivation. The portal vein and bile duct were cannulated, with the time of hypoxia during the dissection procedure restricted to about 30 sec. The perfusion fluid was Krebs bicarbonate buffer containing 4 per cent bovine serum albumin (fraction V, Sigma Chemical Co.), 5 X 10-5M EDTA, and 10mM L (+) alanine. This was filtered through a Millipore filter (0.45,.) immediately prior to use. Ini-tially, the recirculating volume of medium was 100 ml, and 2-ml aliquotswere removed periodically for chemical analyses. Perchloric acid extracts were prepared by adding 2 ml of 8per cent (v/v) perchloric acid to a 1-ml aliquot of perfusate, centrifuging for 10 min at 27,000 9, and neutralizing the supernatant with a solution containing 3 N K2CO3 and 0.5 M triethanolamine. The perfusion apparatus was modified from that described by Miller et al. 9 The equilibration of oxygen between the gaseous and liquid phaseswas imperfect with this apparatus (the affluent fluid being only 45-50% saturated with oxygen), but the high flow rate through the liver (40-60 ml/min) allowed an adequate extraction of oxygen from the medium, as judged from the effluent oxygen tension, which was in the range of 150-200 mm Hg.