SUMMARY

1. The mechanism of action of large doses of glucocorticoids has been investigated in two series of rabbits, the first receiving cortisone and the second an infusion of olive oil to induce a condition simulating 'mobiliza-tion of depot fat ' to the liver. 2. The metabolic turnover of liver phospholipids is enhanced both after cortisone and after infusion for 9 hr. with a fat emulsion. 3. Changes in lipid composition in serum and liver were almost identical after cortisone or infusion of fat emulsion. Levels of neutral fat, non\x=req-\ esterified fatty acids, phospholipids and cholesterol, and also glucose, were increased in serum; neutral fat accumulated in the liver. Neither cortisone nor fat infusion caused any changes in lipids in the aorta. 4. The present findings are taken as evidence of the secondary nature of changes in phospholipid metabolism after cortisone. Cortisone causes pri-marily an accelerated transfer of non-esterified and esterified fatty acids from the depots to the liver during decreased glucose utilization. An increased supply of fatty acids from the blood to the liver after treatment with cortisone leads to their increased incorporation into phospholipid molecules