The amount of prostaglandin E2 (PGE2) in salivary gland of semi-engorged adult female Boophilus microplus, Haemaphysalis longicornis and Ixodes holocyclus were 374.3 pg, 427.0 pg and 825.0 pg per one tick, respectively. It was thought that the PGE2 production is a common phenomenon among ticks. Then PGE2 concentrations in saliva and hemolymph, salivary gland, ovary and gut of fully-engorged adult female B. microplus were compared. The PGE2 concentration in saliva induced by pilocarpine was 40.3 ng/ml and hemolymph was 19.1 ng/ml. Salivary gland, ovary and gut from a tick contains 35.5 pg., 27.0 pg and 2.5 ng of PGE2, respectively.