Blood platelets actively participate in defense mechanisms of the organism. eg. in antiparasitic immunology. The study involved 17 patients infected with Echinococcus granulosus. Blood for analysis was collected twice, before treatment (E1) and after it (E2). Control group consisted of 30 healthy people. The concentrations of β-thromboglobulin and platelet factor 4 were assayed using a set of ASSERACHROM (Boehringer Mannheim) according to the immunoenzymatic method with labelled antibodies. The level of platelet factor 4 (before and after the antiparasitic treatment) indicates platelet activation by parasite