Objectives: The study of mechanism of microvesiculation wich has not been researched yet. We want to show that microvesicles are present in isolates from all body fluids, that microvesiculation is enhanced in patients with gastrointestinal cancer; in subjects whose plasma mediates stronger attractive interaction between membranes, the number of microvesicles in blood isolates is smaller, and that heparin in vitro increases coalescence between membranes and thereby inhibits vesiculation. Patients and Methods: We studied isolates from body fluids of 80 patients (32 with malignant and 48 with non-malignant disease) and 404 healthy subjects. Microvesicles were isolated by centrifugation and washing, counted by flow cytometry and imaged by scanning electron microscopy. Mediated interaction between membranes of giant phospholipid vesicles created by electroformation was assessed by the contact angle between adhered vesicles. Results: Microvesicles were present in isolates from all body fluids considered. The concentration level of micro vesicles in isolates from peripheral blood is significantly higher in patients with cancer of digestive organs (p=0,0002). Number of microvesicles in blood isolates negatively correlates with contact angle between giant phospholipid vesicles adhered due to plasma mediated interaction (r=-0,50, p=0,031). Heparin in therapeutic concentration increases the ability of plasma to mediate attractive interaction between membranes (p<0,01). Conclusions: Microvesiculation is significantly increased in patients with gastrointestinal cancer. Our results are in favour of the hypothesis that attractive interaction mediated by blood plasma is a possible mechanism suppressing microvesiculation of cell membranes. Heparin increases attractive interaction between membranes mediated by blood plasma constituents and thereby suppresses vesiculation. This is a possible mechanism underlying anticoagulant, antimetastatic and antiinflammatory effect of heparin.