The obtained results indicate that the difference in action of tested drugs on platelet aggregation may dependent on the various chemical structures of these drugs. Clozapine, risperidone and haloperidol are structurally diverse, and they all significantly reduce platelet aggregability induced by collagen. On the other hand, a close structural analog of clozapine - olanzapine - did not inhibit platelet aggregation. However, mechanism of antipsychotics action on blood platelets is not clear. Moreover, it seems that clozapine, risperidone and haloperidol treatment due to antiaggregatory action may have even some antithrombotic effects.