The process of fat mobilization has become accessible to study in man with the recognition that the albumin-bound nonesterified or free fatty acids are the major form of transport of lipid moving from the adipose tissue depots to the sites of lipid utilization elsewhere. Previously, information concerning fat mobilization was derived primarily from animal studies. The animal studies have been extensively reviewed elsewhere (1) and will be mentioned only when human studies have only incompletely settled specific issues. During the past five years a number of observations have been made in man which now merit review and which permit the