We have studied in vitro the ability of the Siberian cedar crust (SCC) extract (Pinus sibirica Du Tour) and arabinogalactan sulphate (AGS) extracted from wood of Siberiam pine-tree (Larix sibirica Ledeb.) to increase the human blood plasma coagulation time and also to inhibit the amydolytic activity of thrombin (aIIa) and the coagulation factor Xa (aXa). A method has been developed by means of which SCC increases the aXa activity by a factor of 3.7 and the aIIà activity by a factor of 2.5. The AGS preparation increased the blood plasma coagulation time in the test for activated partial thromboplastin time. An effective concentration, at which the time of plasma coagulation was increased by a factor of 2 (in comparison to the control) was 2.94 +/- 0.33 mg/ml. AGS did not exhibit the ability to inhibit the Xa activity.