We purified apyrase (adenosine 5’-triphosphate diphosphohydrolase),
which is a non-specific inhibitor of platelet aggregation by virtue of its action on adenosine 5’-
diphosphate. We isolated and characterized the platelet-activating factor antagonist and also
identified and recovered an inhibitor of coagulation factor Xa from leech saliva. This report
summarizes our findings and those of other investigators, as well as the experience of one of us
(A.E.) in leech therapy.