The uptake and utilization of [1 -14C]glycerol was determined in pieces of rat epididymal fat-pads incubated in Krebs-Ringer bicarbonate buffer containing albumin. Insulin (200µunits/ml), adrenaline (epinephrine; 0.5µg/ml) and glucose (0, 5, 15 and 20IDM) were added to the medium. Changes in the specific radioactivity of the tracer during the incubation were taken into account in calculating the rate of glycerol utilization. Adrenaline decreased glycerol uptake, whereas insulin plus adrenaline increased it. The rate of incorporation of glycerol into glycerides was decreased by adrenaline and insulin, singly or together. Insulin increased the rate of formation of CO2 and fatty acids from glycerol. The formation. of CO2 and fatty acids was further. enhanced by insulin plus adrenaline. The decrease in glycerol uptake induced by adrenaline, the decrease in incorporation of glycei;ol into glycerides induced by insulin and insulin plus adrenaline and the synthesis of fatty acids were dependent on the presence of glucose in the medium. Thus insulin and adrenaline act on glycerol utilization in adipose tissue and some of their effects are ~ediated by action on glucose metabolism, but others are independent of this.