Investigations into the antihaemostatic properties of the salivary glands and midgut regions of the bloodsucking insect, Stomoxys calcitrans, revealed an interesting repertoire of activities. The reservoir zone of the anterior midgut region was demonstrated to contain a potent anti-thrombin, confirmed with chromogenic substrate analysis, and monitored using the Activated Partial ThrombopJastin Time (APTT) assay. Further investigations revealed the anti-thrombin activity may correspond to protein bands 26kDa and 34k.Da in size, which it is proposed may form a protein complex. The haematological requirements for a secondary inhibition system are discussed, and the evolutionary and digestive advantages of these activities are proposed. The midgut reservoir zone and salivary glands were also demonstrated to inhibit complement-mediated haemolysis. Midgut surfaces, such as the glycocalyx, and the chitin of the peritrophic matrix, would provide an ideal environment for complement to undergo contact activation. It is suggested that the inhibitor provides protection for the delicate endothelial cells, whose membranes are extremely active during and after a blood meal, and to ensure that erythrocytes contained within the blood meal remain intact. The salivary glands were demonstrated to contain a FXa inhibitor, also confirmed using a chromogenic substrate assay. In addition the presence of a putative apyrase activity is reported, demonstrated using degenerate primers of a highly conserved sequence to screen a cDNA library. Preliminary (unpublished) studies also demonstrate the inhibition of ADP-induced platelet aggregation, indicative of apyrase activity. The demonstration of a potent salivary vasodilator, antagonistic to the vasoactive effects of adrenaline, is also reported. Abundancy screening and suppressive subtractive hybridisation techniques identified a putative genetic sequence from a cDNA library. The gene fragment demonstrated extremely high correlation to antigens identified in the saliva of the tsetse fly, and the venoms of wasps, hornets and fire ants.