Anticoagulant activities against the extrinsic and intrinsic coagulation pathways were identified in salivary gland extracts (SGE) prepared from four tabanids <i>(Hybomitra muehlfeldi, Tabanus autumnalis, Haematopota pluvialis, Heptatoma pellucens). </i>All extracts prolonged human plasma clotting time in a dose-dependent manner and inhibited thrombin activity in the chromogenic substrate assay. Horsefly SGE did not inhibit factor Xa. Partial purification of SGE proteins using reversed-phase high-performance liquid chromatography revealed species-specific differences in the elution profiles and range of fractions with anticoagulant activities.