Endotoxins may interfere with platelet aggregation by interacting with the platelet membrane. The aim of this study was to evaluate the effects of tetanus toxin, Salmonella typhimurium porin, and bacterial lipopolysaccharide (LPS) on platelet aggregation induced by ADP and thrombin in vitro. Spontaneous platelet aggregation and platelet aggregation induced by ADP and thrombin were measured. Our results show that Salmonella typhimurium porin and bacterial LPS enhanced human and rabbit platelet aggregation induced by ADP and thrombin. Tetanus toxin did not affect platelet aggregation.