The presence of anticardiolipin antibodies (aCL), von Willebrand factor activity and platelet function was studied in 35 patients with systemic sclerosis (SSc) scleroderma and 22 healthy controls. aCL positivity was observed in no patient with SSc or controls, whereas beta-thromboglobulin and platelet factor 4 levels were significantly higher in patients with SSc (p less than 0.001 and p less than 0.002, respectively). Furthermore, plasma from patients with SSc had a greater degree of aggregation to adenosine diphosphate 1 microM (p less than 0.05) but not to collagen or arachidonic acid. The plasma of patients with scleroderma also had increased von Willebrand factor activity compared with controls (p less than 0.001). We conclude that aCL appears not to play a central role in the pathogenesis of vascular and hemostatic alterations in SSc.