AbstractDuring trivial flight in locusts, carbohydrates are the main energy source for the flight muscles, but during long‐term (migratory) flight, lipids mobilised from the fat body are utilised. The supply of fuels to the flight muscles, and the balance between fuels, is determined by peptidic adipokinetic hormones, AKH‐I and AKH‐II, released from the corpora cardiaca. These peptides also indirectly effect changes in lipid‐transporting mechanisms in the haemolymph, and regulate a lipoprotein lipase necessary for lipid uptake by the flight muscles. The sequences of the AKHs of locusts are known and they are members of a family of invertebrate neuropeptides. Extensive structure/activity studies for the action of AKHs on lipid mobilisation have been carried out and, together with studies on secondary structure, the structural features necessary for biological activity are being elucidated. Such information will be of great importance in receptor studies for these hormones, and in the development of powerful agonists and anta