Interleukin-15 (IL-15) administration to rats resulted in an important decrease in carcass fat (27%) and, consequently, in white adipose tissue mass. This decrease was linked with a decreased lipogenic rate (per g of tissue) in both adipose tissue (53%) and liver (36%). The decrease in hepatic lipogenesis was associated with lower hepatic citrate levels (49%) and a reduced activity of lipogenic enzymes. The results presented here further demonstrate the involvement of IL-15 in lipid metabolism. Thus, IL-15 seems to be able to modulate de novo fatty acid synthesis, possibly by influencing citrate tissue levels, an allosteric activator of the key lipogenic enzyme acetyl-CoA carboxylase.