The data reported by Krauel et al show that fibronectin could decrease the formation and the size of platelet factor 4/heparin complexes (PF4/H), the risk of immunization to PF4 of heparin-treated patients, and platelet activation induced by HIT antibodies (B). Therefore, low-plasma fibronectin levels could be a risk factor for higher levels of antibodies to PF4/heparin complexes and for HIT (A).