Hepatectomy and nephrectomy in the rat produced an increase in blood glycerol levels which was observed before the fall in blood glucose. The disappearance of total radioactivity from plasma after the i.v. injection of either (U-14C)-glycerol or (U-14C)-glucose in these animals was slower than in their sham operated controls. Total radioactivity in plasma was always lower after (U-14C)-glycerol administration than after (U-14C)-glucose. The loss of either tracer from plasma in the eviscerated animals was followed by the appearance of 14C-lactate, demonstrating their rapid metabolism. The radioactivity appearing in the water soluble fraction of lumbar fat pads was increased in eviscerated animals while in the lipid fraction it was reduced from both tracers. These results show that adipose tissue is able to metabolize small quantities of glycerol directly in vivo. The use of both (14C)-glycerol and (14C)-glucose by skeletal and heart muscles was enhanced in hepatectomized rats but the effect on synthesis of labelled glyceride glycerol was greater for (14C)-glycerol, suggesting its important role in the esterification of fatty acids in these tissues.