A series of 5 substituted 3 pyridylisoxazoles were synthesized using [3+2] cycloaddition of nitrile oxides to alkynes with variation of substituents at position 5 of the isoxazole ring without additional synthetic stages and with retention of 2 pyridyl , 3 pyridyl, and 4 pyridyl substitu ents at position 3 of the isoxazole ring. Substituted pyridylisoxazoles are the potential anti aggregatory agents showing in vitro activity in the concentration range from 1•10 -6 mol L -1 to 1•10 -4 mol L -1 toward the human platelet rich blood plasma with arachidonic acid being used as the inductor of aggregation. These compounds do not act as cyclooxygenase or thromboxane synthase inhibitors, nor as thrombin inhibitors.