The influence of new synthetic peptides ARGDS-NH2 and RGD-dFK (synthesized by the fermentative method) and VPNLRGDLQVLA (a fragment of the foot-and-mouth virus's surface peptide) on the ADP-induced human platelet aggregation in vitro was studied. All peptides were found to inhibit the human platelet aggregation, but the synthetic peptides (ARGDS-NH2 and RGD-dFK) showed the most pronounced effect. Significant decrease in the platelet aggregation was observed at their concentrations within 0.1-10 mM. ARGDS-NH2 and RGD-dFK inhibited the platelet aggregation stronger than the reference drug pentoxifylline at equivalent concentrations.