Ultimately, we seek to understand how saliva of arthropods contributes to the interaction of vectors with vertebrate hosts, both in regulating the quantity of secretion delivered to the host and in modifying the physiological response of the host to the bite lesion. Toward this end, we shall investigate the (1) events leading toward salivation, (2) pharmacological properties of saliva and (3) the role of saliva in blood finding and blood feeding. Mosquitoes and ixodid ticks will provide our main subjects for study; but, other arthropods, including sandflies, blackflies and fleas, will be included in certain studies. In particular, studies on mechanisms regulating salivation in mosquitoes will: (a) determine salivary levels of mosquito apyrase in different feeding modes, (b) describe the action of agonists inducing mosquito salivation and (c) define the innervation of the salivary glands. Pharmacological studies will investigate: (a) properties of the saliva of blackflies and fleas; (b) the mode of action of the erythema inducing factor (EIS) of Lutzomyia longipapis, (c) the presence of prostacyclin and leukotrienes in the saliva of a tick and (d) the mode of action of an anti-complement activity of tick saliva. Studies on the role of saliva in feeding will examine the tolerance or resistance of different hosts to repeated ixodid tick infestations and the role of saliva in such processes. This work explores the suggestion that saliva of hematophagous arthropods mainly serves an antihemostatic and antiinflammatory role during blood-finding and blood-feeding.