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1. Isolated sheep foetuses of 72-146 days conceptual age (155-4840 g) have been maintained for periods up to 325 min on an artificial circuit where the placenta has been replaced by an oxygenator.2. Measurements made during the period of observation included heart rate, femoral arterial pressure, umbilical blood flow, blood gases and pH; plasma and urine concentrations of glucose, fructose, lactic acid, urea, alpha amino nitrogen and electrolytes.3. The circulatory, metabolic and renal conditions of the isolated foetus were found to be similar to those of the exteriorized foetus with intact placental connexions. However, in the later stages a terminal hypoxia developed. This was due to a progressive diminution in umbilical blood flow caused by umbilical arterial constriction.4. The young foetuses removed glucose from the circulation and seemed unaffected by the consequent hypoglycaemia. If the glucose removed was completely oxidized it would account for much of the estimated oxygen consumption. The blood glucose concentration in the older foetuses, on the other hand, did not fall and sometimes rose. Renal excretion of glucose was very small.5. Fructose was usually slowly removed from the circulation and under no conditions did a rapid removal occur. Renal excretion accounted for about half of the fructose disappearing from the apparent fructose space. It is therefore suggested that a small utilization of fructose occurs in foetal tissues but this could account for only a very small fraction of the estimated oxygen consumption.

1. Sheep foetuses over the age range 105-142 days and maintained on an extracorporeal circuit removed exogenous acetate at 2.0-4.9 mg/kg.min.2. Urinary loss of acetate was less than 12.5% of the administered amount.3. The rate of acetate removal appeared to be unaffected by the addition of glucose to the circuit. The removal of glucose also seemed to be unaffected by the presence of acetate.4. A decline in the plasma concentration of free fatty acids and ketone bodies was also observed during the perfusion.5. It is concluded that under these conditions acetate may have accounted for about one half of the oxygen consumption. The contribution of free fatty acids and ketone bodies must have been small. The relevance of these findings to the nutrition of the foetus in utero is discussed.