The vectors of filariasis, mosquitoes and blackflies, are capable of mounting a defence response to the infection. This selective review describes the molecules that are involved in these immune systems. Several antibacterial peptides are known to be induced and secreted into the haemolymph by the fat body and the circulating haemocytes. In addition, haemagglutinating lectins with carbohydrate specificities to the surface of the developing filarial larvae appear. Activation of a range of proteases occurs rapidly as does activation of the prophenoloxidase pathway. The possible roles of these and other molecules is discussed, together with mention of a working hypothesis as to how these molecules may be regulated.