Circulating blood monocytes, which are a source of foam cells contribute to the vascular lesions. Von Willebrand factor (vWF) is an adhesive multimeric glycoprotein that is synthesized only by endothelial cells and megakaryocytes. In the present study we assessed the ability of human platelets to secrete vWF after incubation with blood monocytes in vitro. Monocytes derived from blood of healthy adults were cultured and next incubated with washed platelets. von Willebrand factor antigen (vWF:Ag) was measured in the supernatant by Laurell immunoelectrophoresis. The study showed that Triton X-100 treated platelets released 82-112% of vWF:Ag. The levels of vWF:Ag in the supernatant with untreated platelets and incubated with monocytes without LPS were respectively 36-48% and 45-72%. After incubation washed platelets with LPS stimulated monocytes a significant decrease in vWF:Ag level was observed (7-11%).