In experiments in vitro comparison of influence vasopressin and its analogue DGAVP on platelet aggregation is lead. It is shown, that peptides cause aggregation at addition both to the human, and rats platelet rich plasma. In human plasma DGAVP is much stronger inductor of aggregation, than vasopressin, whereas in rats plasma effects of peptides aren’t different. Besides vasopressin and DGAVP considerably increase thrombin-induced aggregation of rats washed platelets, but do not influence on ADP-induced platelet aggregation. Thus, multifunctional action of these peptides on platelet aggregation can be caused both their direct interaction with platelet, and possible synergic action of peptides with others agonists.